Why all of those cards have same amount of ROPs?

So far I had those graphics cards since the day I touched a computer...

ATI Rage 128 PRO 32MB
Nvidia MX 4000 128MB
ATI 9250 PRO 128MB and a 256MB later
Radeon X600 PRO 128MB
Radeon X1300 PRO 256MB
Radeon HD 4350 512MB
And now got a Radeon HD 5570 1GB (Turks cut down version)

Except the 1st one, all the others had 4 ROPs with different other specifications. And when I look through the release years of those cards they are differs from 2003 to 2010 (except rage 128). So my question is why have they used same amount of ROP units for all of them? Does it mean m new 5570 can be slightly comparable with those older cards? Or having only 4 ROPs doesn't matter at all?

Old X800 XT had 16 ROP units so can it beat all of those cards I listed above?