Well, i would say too that buprenorphine (Subutex) can be more easily physically addicting: tramadol is a pretty weak agonist at mu opioid receptor, and the amount you can safely take daily is in theory no more than 400 mg due to the SSRI part of the effect, so it's both weak and kind of self-limiting. Buprenorphine on the contrary binds very tightly to your mu receptor and even if it does not fully activate it, is incredibly more potent than tram even without being a full agonist. It is more an opiate, if you like...
Still it puzzles me that you could take almost daily doses of tramadol and not having problems quitting after two years...what were your doses? Maybe, since tramadol is essentially a pro-drug when it comes to the opiate part of the effect, your liver is not very efficient in that metabolization, but still...and anyway, even an SSRI should give some kind of discomfort when interrupted abruptly...
If you are asking if you can do the same thing for such a long time with Subutex and get away with it, i would say no, not at all...
Anyway if you want to do same research about both drugs, you may find interesting stuff and understand things better