Radeon X1800 XT (in this test) has equal performance as nVidia 7800 which is inside PS3, so unless somebody present benchmarks, I have no reason to believe PS3 can be much faster then Intel X4500.
If you recall, the OSS drivers for R500 are far from mature. As the article noted, switching to fglrx roughly doubled performance (and as we all know, fglrx is not the most performant of drivers).
No, a shared-memory chip with a maximum theoretical bandwidth of 12.8GB/s (shared the CPU) is not able to compete with a high-end discrete card. What you are seeing is an artifact of the R500 driver immaturity, nothing more. You cannot really draw conclusions regarding chip performance from that