Hell, to be honest, I think both consoles should have had 1 gig of ram total. The fact that the X360 didn't is somewhat forgivable given it came out in 2005. The PS3 coming out in 2006 just negates any and all excuses for that.
People where complaining about the PS3's price when it was released. The machine having more RAM would only increase the price and people would be even more offset to buy it due to the increased price.