So much of what you say is just speculation Jumbo.
The Cell chip comes in different versions, some more powerful (with more CPUs) than others.
Sony have not stated which version of Cell will power the PS3.
NVidia have not stated what the VPU will be.
HL2 is IMO, the most graphically advanced videogame on the market at this time. Yes it caters for less-advanced cards, but it's also a different beast entirely on the top end ones. A tech demo of the Unreal 3 engine which is running on hardware which isn't even finalised yet isn't comparable. No one has stated minimum specs for this game, again, it's pure speculation.
There might well be a 2 generational gap between what HL2 can run on and what PS3 will have, but you can't state that as fact when
you don't know exactly what will be inside that machine. Regardless, HL2 doesn't look twice as good as games 2 generations ago, I think Quake 3 is far more than 2 generations of videocard back for example.
Sony
always talk absolute shit when preparing their new console. Yes it will be powerful, but the stuff you say is impossible to confirm because no specs have been released yet, it's only speculation. Also, graphics have reached somewhat of a plateau, they can't continually make huge jumps (refer back to the example I gave, HL2 is years more advanced than Quake 3 but there is not the kind of jump we have seen in the past between generations of videocard).
Anyway, just my opinion. If you're going to speculate then I will too, I think the PS3's laser will be a POS

.