It's a combo of his individual greatness, intelligence, and malleability on the court and his foresight, ruthlessness and much maligned (me included) team construction off it.
Are we really still talking superteams after last season?

There was nothing super about that squad that got to the Finals last year and the "super team" he left was chilling at the bottom of the playoff bracket before Bosh went out. As far as level of comp goes, the west has indeed been better however that gap is sorely overblown. West champs regularly run through that conference with ease including the two times Bron's squad knocked them off. Beyond that what squad could he go to on the West that wouldn't instantly become a "superteam"?

Off top the only ones that I can think of are the Lakers and the Suns. And the Lakers got cap room and the #2 pick.