OKC may be the individual team favorite, but they are far and away under dogs to win the WCF. There are just TOO many good teams in the West that can potentially upset them.
The Spurs, Clippers, Memphis and to a lesser degree GSW and Denver all have a legitimate shot at an upset win in a series.
Face those teams twice and the odds stack up against you fast.
Heck, even the probable lower 7/8 seed teams (Utah, Rockets, Portland and the Lakers) could potentially upset any of the front running teams in a 7 game series if they got hot at the right time.
As for Miami, I think the teams that could give Miami the toughest time of the favored teams from the West are Memphis (too much size), Spurs (too much ball movement and experience) and the Clippers (crazy deep), with OKC oddly as the least favored of the four simply due to match ups of play style.
OKC has the best odds to win the WCF, but that doesn't mean their odds are even as good as 50/50 to win the WCF.
Compare this where the East where I think most people acknowledge that Miami is the odds on favorite with a better than 50/50 chance to come out of the East. With the injury to Rondo, who can really challenge the Heat this year out of the East?
The Knicks? Indiana? The Bulls (if Rose is healthy)? And 2/3 of those teams I wouldn't even consider a favorite against Denver or GSW in a 7 game series, let alone Memphis, OKC, the Spurs or the Clippers. Heck, I'm not even sure if 2/3 of those teams would be favorites against Portland and the Houston Rockets.