While you could call this trivially true if you assume that this is a goal of theirs and they are actually trying, I think it misses the reality that operators don't care, at all, whether your device is up to date in terms of the OS once you've signed on for your plan.

It would be a very interesting challenge to attempt an OS that could be kept up to date in terms of base functionality while still allowing carrier bastardization at a different layer. However, this is a goal that, it seems to me, would have best been addressed ten years ago.