Personality theory (MBTI) is supposed to be about what people have in mind when they do things. Temperament (KTS) is supposed to be about what people DO and how often. So yes there is an important difference. In general I think Kiersey's descriptions are superior.
HOWEVER, the more I read Keirsey's descriptions of INTPs and ENFJs, the more I think he is personally biased about those two types. Apparently, keirsey (an INTP) has some sweet ass honey ENFJ wife that's been his lifeline/support for a long time and helped make him the man he is, which probably has influenced his perception of that type. "pedagogue/teacher" type for ENFJ? Hah, no i don't think so, that description is absurd. Maybe to him an ENFJ was his teacher, but that hardly is fitting of the general type. I myself haven't learned jack nor shit of any worth from ENFJs and I know most of you haven't either, except for maybe how to use Fe better to manipulate and counter-manipulate others. "the empath" is the proper term for ENFJ if you ask me, not pedagogue. Oprah doesn't teach others jack shit either, she is a sharer and exposer of feelings/experiences and it stops at that.
He also greatly embellishes the INTP profile, and this is coming from a tested INTP here. "The architect" and his description of INTPs make them seem like godlike creators/designers standing above the other types, even the other NTs. It's just not accurate if you ask me. ENTPs, ENTJs and INTJs all make better engineers and designers than INTPs if you ask me. INTPS are "abstraction whores", more so than ENTPs. "designer of systems"? Bullshit i say, all NTs excel at that. the fact he throws it into the INTPs lap alone is sheer bias.
EDIT: wow this really turned into a KTS rant didn't it? hmmm