LeBron's amazing, but he's not THAT amazing. Especially when you consider who his teammates are. Quick, name the second best player on the Cavs. Got him? Okay, name another playoff team where he would be the second best player. Brown has done an incredible job and easily deserves it.
Besides, the league DOESN'T reward coaches for that, otherwise Phil Jackson would have 9 or 10 COYs instead of 1 (which is a travesty).
As Eric said, there was the first year of Jordan's "retirement", when he was replaced as a starter by (drum roll) Pete Myers - and I think the team lost about 1 more game than it had the previous year.
Of course, he still had Pippen. But having great players doesn't mean you're not a great coach. Dell Harris got swept with Shaq and Kobe. Jackson won three titles with them. Jackson's strength is taking great players and winning titles. Plenty of great players never do that. I wouldn't want Jackson as the coach of my expansion team (although he's gotten a lot better at developing young players) but he's the best ever at taking very good players to titles.