Joubert only did three one time (2006 CoR) but he does still go for two on occasion, most recently in the SP at the Challenge Cup (IIRC). I think Plushenko has never landed more than two in one program because he only does 4T (although he has tried the 4Lz).
FWIW, Joubert hasn't taken whole seasons off, but he has missed quite a few events in recent years due to medical issues.
I just like researching stuff, even relatively meaningless things.
Joubert's miss at 2008 TEB was unintentional - he did plan a quad, but got the pick in wrong IIRC. I know of one competition as a senior where he deliberately did not attempt a quad: 2010-11 French Nats, in the LP.
Either way, pretty cool that they've landed so many quads and are still landing them at age 29 (Plushenko) and 27 (Joubert). I wonder which active skaters have the next highest number.