Well, reading through everything so far and filtering out the obvious misunderstanding of the question and misconceptions about the physics (yeah, I started out studying mechanical engineering though I changed majors) I would have to say that I'm still not entirely convinced that a bicycle is stiffer purely due to a compact frame (notice I changed frame to bicycle as that's really what I meant in the first place - nobody rides a bare frame). I find Caterham's arguments in favor of the compact frame being stiffer the most convincing. Particularly the changes to the rear triangle.

On the other hand, I suspect (though obviously I have to hard proof) that the majority of flex comes from the areas around the head tube and bottom bracket. Chain stays are very narrow and are often ovalized such that they would better resist flex in the vertical plain. Seat stays are just as narrow if not more so and are so close together at the top that I doubt they offer any significant resistance to lateral forces whether the frame is traditional or compact. And while an oversized bottom bracket and stiffer (whether from thicker tubing, larger diameter, whatever) seat tube and down tube will offer increased stiffness, I don't see how angling the top tube down such that it intersects the seat tube at a lower point would increase stiffness. If anyone read Jan Heine's recent tests comparing frame stiffness (all traditional horizontal top tube frames) he theorized that a stiffer seat tube was more likely to cause rubbing under heavy loads because the bottom bracket shell itself deflects. I've had similar experiences with my bikes - my old Bottecchia Special with thick hi-tensile steel tubing would rub like hell and I'm sure I could actually see the flexing when sprinting out of the saddle. My Gran Turismo never rubs and I don't notice any flex even though it's made of thinner Columbus SL tubing.

Honestly though, if I were a young person buying a bike today and had no prejudices either way, I think the compact frame offers sufficient advantages to make it a viable choice, maybe even a better choice regardless of whether it's actually stiffer as a direct result of the design. As it stands however, I'm an old coot who thinks traditional horizontal top tubes just look so much better (along with lugs and wheels with lots of spokes, and polished aluminum doo-dads and chrome, lots of chrome) that I would choose a traditional frame anyway. But I do like to keep up with the latest technolgy and understand why it may (or may not) be better, hence this post.

BTW - Jan's tests also indicated that a stiffer frame was not necessarily better at power transfer but you'll have to read his article and make up your own mind.