There seems to appear question about operating systems/architecture in general (like spin locks or memory handling). Are those on-topic (and therefore in possible clash with operating system development) or off-topic?
That's a good question. I found them both interesting, but I'm interested in programming; they don't really seem on-topic for a site that helps people with *nix. I guess if it was a question about how the Linux kernel specifically does something that makes sense, but general questions about what a spin lock is probably aren't
I understand these questions as having an implicit “on a typical unix system” (just like when someone asks for software do do X, I assume that running on unix is a requirement even if that's not explicitly stated).
I do consider questions about the design of unix systems to be on-topic (they have even more legitimacy than history questions, which I also support).
I'm not a big fan of Sen and Renjith's questions, but my problem with them is not topicality, it's that they tend to ask overly broad questions. I think they would benefit more from reading a book or Wikipedia, and asking more specific questions about point they don't understand here.