He's also very slow, though. Aerodactyl, on the other hand, usually runs Rock Slide over Stone Edge, from what I've seen.
Oh, and 70*.90=63, 100*.80=80.
It's really only 17 BP, or 25 with STAB.
It's already been proven that factoring accuracy into BP doesn't work, you might survive an 80 BP attack, but not an 100 BP attack. The only place this is works is for probabilities of a OHKO/2HKO, which is why you hear that Gengar has a 49% chance of 2HKOing Blissey instead of a 100% chance. However, everytime Focus Blast hits Blissey its a 120 BP SE attack.