Leave John alone! He's only telling the truth and speaking in regard to the specifics of id Tech5.
The PS3 does have "tight memory" in that it's split between CPU/GPU whereas 360 is universal between the two.
The I/O is a little slower (excluding the HDD) and this matters in this case due to the mega-textures used with Tech5.
The CPU is more powerful than the 360 but when speaking to a games engine, as he is, then the performance is closer due to memory and other architectural elements. Outside games the PS3 is a fair bit more powerful than 360 from a CPU, which is why researchers are fond of linking them to use the CPU power, but with games other limitations constrain the PS3 CPU to a performance level closer to the 360.
Really, by this stage it should be pretty clear to anyone that cares that the PS3 has the better CPU, the 360 the slightly better GPU and the 360 memory design is easier to work with than the PS3's. Due to PS3 allowing more access to the hardware than the 360 - which of course wants developers to use DirectX and middleware - PS3 specific developers like Naughty Dog can get access to and squeeze out that little extra potential the addition CPU power of the PS3 offers.
This guy is not just a programming legend but he pretty much always speaks honestly and without regard to marketing, so let's cherish that in an industry that is given over to hype and white lies positioning from highly paid salary folks.
With Tech5 getting 60fps (or close) was always going to be tough on the PS3 and the 360 too, hence the big install on PS3 and the clear recommendation that you should install on the 360 too (and I'd advise it myself after playing RAGE on the 360).
As it stands, a full install on the 360 runs a bit better than the PS3 partial install however the PS3 outperforms the 360 with no install in a number of areas.
Really, the game looks good for what they're doing and the frame rate is amazingly smooth (as are the animations) on booth consoles compared to most FPS today.
Rage, as with all multi-platform titles, is never quite going to pip a fully custom engine written by equally talented folks to id, but like BF3 and the new Frostbite 2.0 engine it does a pretty good job overall IMHO.
Good grief both the PS3 and 360 have limitations and it should be possible for developers to speak to them without silly overreactions from people who clearly know close to zero technically about what's even being discussed.
Try to be reasonable... its easier than you think...
