well for the u.s., gta4 came around the same time that gas prices have seen a drastic increase in cost, with numbers going up ridiculously on some days. The ineffectiveness of gta4 to sell consoles could not be that people don't like the game, they're simply looking at their priorities:
a few hundred dollar system with a few great games...or saving it and using it to pay for going to work and buying increasingly expensive food products