LWN, who are generally pretty well-informed on free software matters, have so far reported this only in passing. They do note that the change was released in such a manner as, arguably, to make it likely to be missed; read into that what you will.
Examination of Greg's patch reveals it's not just .ru addresses; some maintainers with gmail addresses were also removed, so this doesn't look like an uninformed snap decision. No public discussion happened beforehand, and Greg's patch (and Linus' followup) contain nothing other than a single sentence about "compliance", so as has been pointed out we can't (yet) know what motivated this. I note it doesn't say "sanctions compliance"; it could just as easily be HIPAA or SOX compliance, though I've no reason to think that it is.
My speculation is as uninformed as the next guy's, but I note that there have recently been other attempts to insert malicious software into ubiquitous parts of the Linux system infrastructure (such as this one). Linus is also known to rely heavily on his maintainers; if you can get something cunningly-malicious past a maintainer, there's a non-zero chance it ends up in the official tree.
I certainly haven't seen any attempts to make a blanket policy banning all Russian developers from contributing to the kernel, and in any case such a thing would be very hard to police. So this change looks to me like a reasonable attempt to make sure that the penultimate line of defence against malicious code entering the kernel doesn't contain people who, though no fault of their own, are in a position to be leant on by a government with a track of record of heavy leaning, in order to force them to pass to Linus something which shouldn't be so passed. It also takes those poor maintainers out of that particular field of fire.
As for the whole Linux-Foundation-is-controlled-by-the-US-gummint thing, well, it certainly has to obey US laws. But Linus is the guy with final say on what goes into the kernel, not the Foundation, and I don't think the Foundation is so foolish as to assume that their paying him means they get to tell him what to do in that regard. In the limiting case, Linus still has Finnish citizenship, so as an EU national has nearly thirty other countries he could go and live in if the US government decided to get hot and heavy with him.