its not just the size of the wire, its how long it is. a couple feet of 4awg can take 2000w but a full 15ft run wont. do yourself a favor and go to bcae1.com click on "wire" on the right. i think its number 17. itll tell you everything you need to know.
but in the game of overkill, as you put it, a lot of companies do use 1/0 inputs. others use 4awg. probably because they know these are not amps for competition. they will get music and as we all know, music is dynamic. 90% of the time the amp wont be pulling its max current so 1/0 is especially not needed.
but another plus side to bigger wire is; its made of copper. copper stores electricity. having more copper acts like a little capacitor. just a little more burst energy to help run the system.