I think its because most people use the middle chainring position to achieve the desirable chainline. 32t generally being the smallest middle ring size.
Yes, this probably, although if you're using a normal cassette type hub you should be able to move the sprocket in far enough to achieve a correct chainline with the granny ring position. If you're using a freewheel or a single speed cassette type hub (like Hope or Chris King trials/SS) then you might not be able to get the sprocket inboard enough, as the wheel has less dish.
Another thing to consider is that, for a given pressure applied at the pedal, chain tension is higher the smaller the sprocket/chainring sizes become, resulting in higher tooth loading just when you have fewer teeth engaged with the chain anyway, so more wear, less smoothness.
It hasn't been a problem to me with a my 28T HBC chainring, which is pretty much as good as new after two years, but I'm old and pretty mediochre in my power output.
Hopefully you're not.....