If you mean things like I can't use Fusion Brain on it, that's true. But that is a specialized piece of hardware and a very good argument for why you might want to run Windows on a CarPC.
As for backwards compatibility, well, I can run anything all the way back to OS 9 which is pretty ancient. Everything else can be run on an emulator.
I think we have been pretty respectful of each other as a community because we're all experimenters. I'm going to close this thread not because it is out of control but precisely because it isn't. I think we've aired out the differences enough for the OP.