For AMD parts it's pretty easy -- we release detailed block diagrams to the review sites with each new HW generation and that info ends up on the Wikipedia pages with pretty decent accuracy.
For the Intel parts there's a lot more reading between the lines required -- seems to be consensus that the HD 4600 has 2 ROPs but no indication how wide they are. The EUs seem to be 4-wide ALU sets and various slides talk about "hashes" or "quads" of pixels, which argues for 4 pixel wide ROPs (8 total). The raw fill performance seems to support that as well.
To add to the complication, the pixel processing blocks (we call them DB/CB for depth/colour buffer) often include more units for Z & stencil ops than for colour operations, the idea being that a lot of "potential pixels" don't get drawn because they are obscured by already-drawn content (reflected in the Z buffer). The AMD parts typically support 4x the number of Z ops as colour ops, not sure about Intel. The implication of this is that you have to be careful which synthetic benchmarks you look at.