Why is weight no longer an issue after 200lbs?

I've always wanted to know this. With all of the divisions out here to confuse the crap out you, why don't they have a weight class for 200-210, 211-220 and so on like the other weight divisions. I guess 200lbs is just as heavy as 270lbs(joke). It always seemed to me that the regulation of Boxing weight stops at the Heavyweight division. Jones was 200lbs(if that) when he fought a 233lb(I believe) Ruiz. Thats a 33lb weight advantage. Why not have Floyd Mayweather mix it up with Tarver or Johnson? I'm ignorant on this matter and would like to know what is up with that.