Here are some yogurt starters from a popular internet retailer :link
My questions are :
1> Are the microbial colonies developed in homemade yogurt using the above any different than that using a small portion store bought (active) yogurt ?
2> Is the “probiotic potential” of yogurt enhanced when you use the above gourmet starters ?
I can’t guarantee 100% exact identity, since there could theoretically be some variation between strains, but in any case they’re all the same “bug”. All those different “kinds” claimed by different yoghurt makers, the same bug as well.
Frankly I’d expect more variation from which kind of milk you use than from whether you get your lactobacillus from Danone or from Homeyoghurts Organicus.
Different starters have a different collection of cultures. The two basic “bugs” are Lactobacillus bulgaricus and Streptococcus thermophilus. But there are various combinations using different bacteria. See here.
And looking through various sources online, it appears that strains of L. delbrueckii subsp. bulgaricus vary in terms of acidity and thickening power, but I’d venture to guess that the biggest flavor differences between yogurt cultures would be the presence of different bacteria. Like, for example, this creamery makes their yogurt with four different strains of bacteria. In addition to the basic two mentioned above, they also use Bifidobacterium Lactis and Lactobacillus Acidophilus.
So, if there’s a brand that has the taste you want, use it as your starter?
Sure, you can absolutely do that. As Nava notes, there are other factors at work in terms of the taste (the milk, obviously, as well as the temperature, how long it’s fermented) but it’ll give you a good start.
A single species can have a lot of variation. It’s even more true of bacteria, where “species” can pretty hard to define, since gene swapping can happen between bacteria that aren’t closely related. So, it’s plausible that one strain of bacteria might have benefits over another.
But I sure wouldn’t take a merchant’s claim for it.
And you don’t even need starter to make yogurt. I’ve done that a number of times, back in college days, finding a glass of milk from a week ago sitting out. However, I refrained from eating it. Well, it sure looked like yogurt, but now we’ll never know. 
Unpasteurized milk will eventually ferment and make sour milk–something a bit yogurt-like or kefir-like. Pasteurized milk, well, that spoils. You might get lucky and happen to get the right bacteria in there, but, typically, unless you inoculate it with specific cultures, pasteurized milk is going to spoil. Unpasteurized milk already has some good souring bacteria living in there, so it sours rather than spoiling. Spoiled milk tastes terrible. Soured milk tastes fine, like cultured buttermilk.
It had the consistency of yogurt, not sour cream. And, it didn’t always happen; sometimes I got varicolored results, which I definitely didn’t drink. My suspicion was that there’s acidophilus floating around, but I sure didn’t bet the farm against the possibility that there were other more nasty critters in there, or that something that looked, stirred, and smelled like yougurt was actually something nasty. I had taken a bioengineering course where I learned the correlation between lactogens and pathogens.
Eventually I got out of the habit of leaving a glass of milk sitting around.
One could argue, based on this logic, that buying brewer’s yeast when making beer at home is “woo”, since you get the same results by just letting fresh apple juice sit on the counter for a few months.
Uh, no. The OP’s contrasting two different sources of existing yogurt cultures (store-bought yogurt vs. starter), not a commercial source vs. “random accretion.”
I’d say they’re woo to the same extent that probiotics are woo: probably somewhat beneficial, but almost certainly not as beneficial as their proponents make them out to be. I don’t doubt that some of those starters make better yogurt than a scoop of Dannon would, and maybe some of them are even slightly better for you than most store-bought yogurt. But I wouldn’t trust the marketing behind these products to tell you which ones are really better, or what the actual health benefits are.
If you’re replying to my “logic”, you’re absolutely correct. I was just having fun, not contributing much to the fight against ignorance.
I use the term “logic” here very, very loosely. 
<== smiley I should have included above, I suppose. Oh wait, I did include it; I just mistyped it.