Rondo's FTs haven't improved, but I think that his overall outside shooting has this season.
Also, while I think we'd all like to see Rondo improve his overall shooting and free throws, I don't think his poor results are due to a poor work ethic. It's clear that Rondo has worked on his game a lot since his rookie year.
Lots of guys don't improve parts of their game in their career; sometimes guys just don't have a skill, and never develop it. I mean, if shooting was such an easy skill to learn, everyone would be good at it, right? And yet, many extraordinarily talented players never get the hang of it, including the man you cite, Shaq.