There is definitely a difference among the three but I can’t tell you what the difference is in the tobacco used or the manufacturing process. I smoked a pipe for a couple of years and most pipe tobaccos have some sort of flavoring, varying from dry to sweet, fruity, etc. (analogous to wines). Beginner smokers like the cherry crap. I liked the more earthy varieties. Pipe tobacco is moister than cigarette tobacco. Cigars are also stored in humidors to control the moisture. You never heard of anyone doing that with their Marlboro Lights.
Cubans are highly sought-after because of the tobacco grown there, but a lot of cigarette tobacco is grown in the South (VA, NC). So there must be a difference in the varieties of tobacco used, but I don’t know the details.
Pipe tobaccos are of very different stock. There are Virginias, Burleys, Orientals, etc, which all taste very different since they are not only different types of tobaccos but also grown in different places which adds to the taste very much. If you start to grow orientals plants in the US, you do not get the “oriental flavor”, the Greek and Turkish plants need to grow in the rocky soil where it has been harvested for hundreds of years (they tried it with dissappointing results) to get the taste the connoisseur wants from an oriental. There are differnt oriental leafs, too.
Every category – which usually are cured in different ways – has lots of subcategories which taste and smell different (for instance, US Virginian and Virginia from Zimbabwe, and how those leafs are cured are of immense importance), and so on. On top of this, there are specially cured tobaccos which adds distinctive flavours like Perique in the US, Latakia in Cyprus and Syria (a very noticable distinction when you smoke those two), and Kentucky. The producer mix these types of tobaccos and get blends of a wide variety of taste and smell (English, Balkan, etc). With cigarettes, you don’t go through all these hassles, you just need some good burning often low quality burleys and that’s that.
With pipe tobacco, you can also add “casings”, like whisky, maple syrup, cherry, and so on and so forth, making so called “aromatics”. One way of define an aromatic would be, a pipe tobacco which won’t smell like tobacco.
Pipe tobacco is as complex and interesting as wine, there are so many different flavours to experience there is no end to it. It is nothing like smoking a cigarette, certainly not in taste but not in smell either (though some types of non aromatics just smell like a cig to non pipe smokers).
My dad smoked a pipe usually and sometimes a cigar. I believe both are plain tobacco, while a cigarette is wrapped in paper, which may distinguish it from the other two.
On pipe vs, cigar, I’m not quite sure why they would smell different. Someone earlier suggested different types of tobacco. Perhaps burning ‘ground’ or shredded tobacco in a bowl is different than burning rolled whole-leaf tobacco in the open. Now that I think about it, with a cigar you may be smelling more of the “pre-inhaled” smoke, while with a pipe you may be getting more of the post-inhaled scent.
I kind of liked the smell of a pipe of tobacco, while cigars and cigarettes always struck me as kind of sharp or acrid. I don’t smoke myself, but I’m not strongly anti-smoker either.
Cigar leaves come from a different kind of tobacco plant than pipe tobaccos do (the varieties of which have been explained well by Wakinyan, above)–for example, two varieties of Cuban tobaccos used in cigar production would be Corojo and Criollo. But cigar tobacco production is not limited to Cuba, and cigar tobacco is grown in a number of places: for example, Ecuador, the Central African Republic, Honduras, the Dominican Republic, and the Phillippines, among other places. Each place and its growing conditions, can affect the eventual flavour and aroma of the tobacco.
Curing cigar tobacco also follows a different process from that which pipe tobacco undergoes. Leaves are never pressed or steamed, as pipe tobaccos sometimes are; but rather are bundled and stacked, with the stacks being “turned over” every so often so all the bundles spend an equal amount of time exposed to the air and buried in the stack. There can be other curing procedures as well, and the whole curing process can take up to a year before the tobacco is ready to be rolled into a cigar. Even after rolling, aging should occur, as the different tobaccos used in the blend need time to “marry” if they are to reach the flavour and aroma profile intended by the blender.
The end result is something that does not smell like a pipe–which makes sense, as the tobaccos are different, they come from different places, and they are cured in a different way.
I should add that there is a world of difference between how cigarette tobacco, and pipe/cigar tobacco is cured.
We’ve discussed pipe and cigar tobacco curing above, but it is worth noting that cigarette tobacco is not nearly cured the same way. Generally speaking, cigar tobacco is cured so as to leach out as much nicotine as possible during the curing process. Pipe tobacco, not so much, though some nicotine remains. But cigarette tobacco is cured in such a way as to “lock in” the nicotine that occurs naturally in the plant. “It’s toasted” is more than Lucky Strike’s slogan; it is a description of how cigarette tobacco is cured. And all cigarette tobacco is toasted; this speeds up curing while locking in nicotine content.
Nicotine tends to taste and smell bitter, which is probably why the OP can detect a difference between the three sorts of tobacco: cigar, pipe, and cigarette. Cigarettes have plenty of nicotine, pipes somewhat less, and cigars very little.
Anyway, that’s just my educated guess as to the OP’s question.
These are all good points, but I think the simplest answer is, “it’s the paper”.
My SO has been doing roll your own (RYO) smokes…you go to the store and they’ve got rolling machines (either huge expensive automatic rollers or machines where you roll one at a time) and they are, as I understand it, using pipe tobacco in cigarette tubes. They smell like cigarettes.
When he’s low on smokes, he uses the “shake” that inevitably falls out of the tubes as the tobacco dries out. He smokes the shake in a pipe, and it smells like a pipe.
And yes, he does use humidifiers for the cigarettes - little “water pillows” full if ultra absorbent gel soaked in water - you don’t need them for regular manufactured cigarettes, but that’s because they’re packaged in 20 smoke packs wrapped in plastic to prevent water loss, and you smoke them all before they have a chance to dry out. RYOs are packed in a box of 200, without plastic, and will dry out before you can smoke them all.