Notice I had quotation marks around skip-proof.
It's not literally skip-proof but there are many records that align the same sample several times so that if there is a physical skip it hops on the exact same segment of the sample that is being scratched--it's pretty effective actually.
As for straight arm turntables, I should've specified that they are being designed specifically for scratching. Of course there have been hundreds of straight arm turntables before these but they certainly can not stand up to the abuse just because the tonearm is straight. You need to also consider platter stability, drive type, torque, pitch controls, etc.
Anyway, back on topic...