Sure they have. Not sure if anything like that would get called out in a beta update, but things of that nature have been called out by Apple in public releases.
In that case, technically, iOS 8.2 didn't bring any performance improvements. Which I guess on the one hand might be difficult to quantify if you for instance remove excess code which makes the UI run a bit better.
Anyway, I find myself seeing that maybe auto-scrolling has improved somewhat with 8.2 in terms of not stuttering as much. It's still not consistent or good enough though.
made structural changes to their infrastructure, which may also explain the widespread outage we saw a few days ago.