The difference I see between optical scanners and touchscreens is that the optical scanner is not needed at each polling place. One optical scanner could tally the votes from several polling places. Also, the optical scanner would only be used by election officials who are presumably trained in its use, where touchscreens are put in front of the general public and as such need to be built to withstand that level of use/abuse.

I once had to cast a provisional ballot due to moving before the election. Simple - 8 1/2 x 11 piece of paper with "president: choice A [] choice B [] choice C []..." They gave you this and a permanent marker. What could be easier? Why can't we use this for all ballots? Maybe with a perforation to separate the marked portion from the instructions.