1) Cost, weight, flat resistance.
2) Obsolete size designations. See
http://www.sheldonbrown.com/tire_sizing.html
3) I used to like Ultremos, but the R series just aren't worth it. Try Continentals
4) Are you talking about the bead? Kevlar is lighter and more foldable.
5) Sort of. Tubes fit a range of tire sizes.
6) It's not the "thinness", it's the weight and gripiness.
7) Incorrect.