I just replaced mine on my R53 with about 30k on it. I replaced the fronts (rotors and pads) because the rotors were out of spec for passing state safety inspection. I replaced the rears because I wanted them to match the front.
I bought ATE Premium One rotors and Hawk Ceramic pads. As a slight upgrade to stock. It cost me pretty much the same as OEM stuff.
Now, to answer your question about HAVING to replace the rotors with the pads - I have heard this before as well.
Here is MY take on it. If the rotors are still thick enough to last you another set of pads, then go for it. But I would use the same kind of pads as the ones you are replacing. (A more aggressive pad, may chew through the rotors faster and leave you with a reasonably healthy brake pad but a rotor that is toast. And when you replace rotors you should definitely replace pads, so you're throwing money away by having to replace a still usable pad)
A driver who is exceptionally hard on his/her brakes might find that this doesn't hold true, but for most enthusiasts I think it's a fair assessment -YMMV.
As a side note, I don't think the Ceramic pads are right for me, they aren't any more aggressive than stock. I've put a couple hundred miles on them and I am thinking I want to go with the HPS pads. The Ceramic's are AWESOME for lack of dust though!
Perhaps you would be interested in my ceramic pads? They aren't cheap, and I'd be willing to make you a deal!
-Ryan