I have had RB since the day it came out and I have not broken the drums pedal... Basically if you don't pound on it, it won't break. Yeah, if you are a drummer already, and are use to hitting that pedal hard to get some sound out of your bass drum, then yes, you will break the pedal. You will also break the GH:WT pedal, and the RB2 pedal... Give it some respect, and don't beat on it and it will last. No, there is no extra "note" on the GH:WT drums that makes the RB drums incompatible. The GH:WT drums only has 3 "drum" pads and 2 "cymbal" pads, HOWEVER, both "cymbal" pads play the same thing (i.e. it doesn't matter if you hit the left or right cymbal, they both do the same action). The RB drum kit has 4 "drum" pads (and the RB2 kit has extensions for 2 cymbal pads, but again they double as the same as a drum pad hit), so in other words, both kits have 5 "buttons", (RB kit has 4 pads + 1 kick (2 cymbal optional); GH 3 pads + 1 cymbal (second cymbal uses same button) +1 kick).
RB also has an elite kit coming, which is really a full electronic drum kit which has a USB connection that will output in compatible controller output as well as the normal MIDI interface. But this is going to be as expensive as a real electronic drum kit, since it is one...
I really wouldn't get the GH:WT kit as it has been said, it really SUCKS. The hits are not accurate at all, it is either too sensitive or not sensitive enough. The pads simply do not work well.
All things considered, if I was to start now and pick what I buy, I would get the RB2 full kit (i.e. guitar, drums, mic, game), and a second RB2 guitar. Now, a lot of people have a preference on the guitar. Some like the GH guitars better, others like the RB guitars better. I am of the prefer the RB guitar. It might not be as durable as the RB guitar (while the original batch had issues, the replacements that were sent out for people with broken ones seem to have resolved the problems). I like the fret buttons about a thousand times better on the RB guitars than on the GH guitar. The RB guitar is just more like a real guitar in terms of sliding up/down the frets, there is no huge piece of fretwire that is going to stop your fingers from sliding up/down a real guitar because your finger is sliding up/down the string which sits on top of that fretwire, but with the GH guitars, you have this huge piece of plastic in the way (to which I took a dremel to help alleviate the issue). The strum bar is better on the GH guitars in terms of tactile feedback, but it certainly makes a lot of noise. I prefer the quieter effect of the RB guitar with the sacrifice of tactile feedback. I mean, this is a music game afterall, I would rather not hear more clicking than I have to from the instruments....