I hate this “feature” also. Really, if my windshield is fogged up, I’m smart enough to turn on the AC to clear it: don’t make it mandatory. Give me the option of running the top level vents without the AC, dang it!
2005 Prius: Windshield defrost, Upper body, Feet, Upper body and feet, Windshield and feet.
I just wish I could figure out how to use the blower without having the a/c on. You know, just have the fan circulate the fresh air without doing anything to it (and using energy).
2006 Ridgeline RTS same here
Current VW & Audi TDIs have an auxiliary electric heater – at least my A3 does. On cold mornings, I’ll get warm air coming out of the ducts before the temperature gauge has even considered moving.
My '46 Willys CJ2A had one. I never used it. I gather gasoline-fueled heaters were fairly common in the first half of the last century.
My 08 S4 has the windshield defrost setting separate from the cabin heater controls. It has the winter package, so I am not sure if this was standard on the S4 or if it is specific to the winter pack.
But plenty of cars have heated seat warmers, and those get plenty toasty. How many watts are those? Yes, it would be more taxing on the alternator which would then require more RPM’s than the engine, but I think it would just be comparable to AC use in the summer.
I’ve got an 08 Prius and can just turn the A/C on/off with touching the A/C button and it keeps the fans blowing. It’s got the recycled/fresh air button too. Looks just like this. (If you click on the speed, it will take it out of the AUTO mode).
A seat warmer requires considerably less power because it is warming a static material. A blower heater must become considerably hotter to transfer heat effectively to the cool air being continually sucked through it. The fuse for heated seats in my car, for example, is 15A for both seats. A regular electric blanket, which is larger than a car seat, might draw between 200 and 300 W, which corresponds to max of 25 A if it were powered by the car. The power equation for DC loads and AC resistive loads is P = V*I, where the power is equal to the voltage multiplied by the current. So, for a given power output, the current required increases as the voltage decreases. Since standard house line voltage is coincidentally 10 times more than a car’s system, any heating device will require about 10 times more current in a car than a house to put out the same amount of heat energy.
It’s the way the ducts and valves are aligned. Since you have 3 options (face,feet,glass) no matter how you align the 3 the two on the ends can’t be used together. Most are aligned FACE-FACE-FEET-FEET-GLASS-GLASS and the duct is two wide so the valve slides left to right giving you the options:
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
FACE-FACE-FEET-FEET-GLASS-GLASS
I suppose they could alter the order of the 3 but you’d lose one of the exsisting combos. Pretty sure they went with the most popular/funtional combos.
I’ve assumed that AUTO means that it will seek to maintain the desired temperature.
Well, turns out I had misremembered - in fact there are only five options, and as the OP says, face and glass simultaneously is not one of them. Unlike the OP, however, I have never felt the lack. When it is set to “glass only”, a small but significant amount of heat still comes out of the fascia vents.
I think Hampshire has hit the nail on the head with the explanation, well done! Of course, it does not have to be done that way, but it must be a lot cheaper than a fully electronic system that would allow all options.
The 2002 Chevy Malibu allows…
Face, Face - Feet, Feet, Feet - Glass, Glass, so it Fits Hampshires Theory.
I dislike warm air blown in my face, so it never bothered me.
I did once read about a person who covered half his radiator with paper or cardboard to allow less cooling in very cold weather to have more heat come into the passanger compartment. You may have seen big trucks with canvas over their radiators, same idea.
On a related note, why won’t my car run the rear defrost as soon as I turn the car on? I have a remote car starter, so I’ll leave the defrost cranked up and turn the car on to warm up, but rear defrost requires you to press a button inside the vehicle to activate it, so I end up with every window defrosted except the rear which is still covered in frost. Is it because I have those strips that get heated themselves running on the window instead of vents?
Can you show us a picture of that? My 1996 Saturn didn’t have it. Seems weird that they would remove a feature like that on a later model.
I believe so. I think those are run on a timer or at least turn themselves off when you power off the car. I’ve heard if left on for too long they can overheat and damage themselves.
The federal government sets the standards as to how you car is designed to operate; section 103 deals with heating and defrosting. Sorry, but I don’t have time to get you a detailsed link to this section right now (time to go do some Friday night drinking! 
Individual car companies interpret the government standards differently and getting sued by someone (or many people) is what drives them to refine their interpretation; thus they all do it a little bit differently.