Look, the guy saw 15-1 odds and intelligently jumped on them.
I've got no problem with the bet. That's simply a matter of economics, although for people who believe in karma (and Simmons claims that he does), betting against your favorite team seems like the ultimate self-imposed jinx. However, if somebody gave me 15-1 odds on the Cavs right now, I'd probably take it. (For the record: the only team I have money on is the Celts, at 4.5-to-1).
My issue, to the extent that there is one, is Simmons continually saying "Cleveland will win the championship". That's fine for an objective sports columnist. It's not fine for somebody who claims to be the biggest fan in the history of Celtics sports. I'm pretty sure that sexyscottish, or any number of Celticsbloggers out there somewhere aren't saying "You know, yeah, even though the Celtics have beaten Cleveland two out of three times this year, I think the Cavs are better." That's not, from my experience, typical "Super Fan" behavior. (And I differentiate between casual fans, fans, and Super Fans / those who "bleed green").
As for last year's Lakers thing, it was pretty convenient to claim "reverse jinx" only after the Celtics won. His position all along was "I want the Celtics to win, but I think the Lakers are much better". Only after the series did he change his tune, claiming the lame "reverse jinx" thing that so many predicted that he would fall back on.
Bill Simmons, Columnist is entitled to whatever opinion he wants. Bill Simmons, Boston Sports Guy shouldn't be openly picking other teams two years in a row.