ya, that's the whole point. the flip chip packaging is one of the major reasons why a near doubling in transistor count while sticking with .15 micron doesn't kill the clockspeed..
as for the P4 @ .18 vs Athlon @ .18 thats a terrible comparison..
first of all, the P4 topped out at I would say 2ghz like u said, but the Athlon is just now topping out at 1.73 I think. I'm not surprised that the higher transistor count package was designed for higher clock speeds, because that's what the pipeline is all about, whereas I don't see anything these days on how many stages the pixel pipeline is on a video accelerator (because as we all know the 8500 and GF4 both theoretically can pump out 4 dual textured pixels PER CLOCK), or anything like that.
I guess that answers the question on why video accelerators are slower mhz wise than CPUs. they have an extremely high IPC (instruction per clock) count..
my point is, ATi doesn't appear to have necessarily sacrificed IPC to achieve the same thing. I mean we all know the GF3 for some reason was a bit quicker clock for clock than the 8500 (most likely a better design, ie, better placement of cache or something), and we all know the reason for the near doubling of transistor counts (adding DX9 compatability).