In the PlayStation 2's case however the massive cost is probably more to do with a shitty MMU rather than Ram/Bus speed. The PS2 has RamBus designed RAM and huge bandwidth (1024bit bus and shit). The reason it needs this is because it has fuck all texture RAM (2MB) so you're moving huge chunks of memory around all the time.
Yeah, memory has not kept up with CPUs in terms of clock speed. Before the 386, there were no caches in PC-compatibles. With the 386, on-chipset caches were first introduced by some manufacturers, and they made a noticable difference. The 486 was the first CPU with an on-chip cache; so the first chipsets didn’t have a cache of their own. When L2 cache were introduced, their contribution to performance was controversial. With the Pentium, however, there was no question that the gap between L1 cache speed and main memory had gotten so large than an L2 cache was an undeniable boost.
Regards