In many respects, this question (and the response) goes to the heart of a concern I'm already developing over the SO family of sites and many of the Area51 proposals - fragmentation.
Yes, the RPi question would be more directly on-topic at RPi.SE(beta) than here. But (as the responses show) the "turf war" is already in place with the view that RPi questions are also on-topic here (and probably elsewhere too).
For some reason, the Embedded Systems proposal (now in committment) is looking very RPi-centric (likelyhood of both surviving is probably slip), and likewise there are several A51 proposals relating to robotics (in one form or the other) when a combined Robotics proposal would make most sense.
Personally, I'd rather see a smaller number of well-scoped but broad-topic sites, than a bigger number of niche sites that will probably wither.