I don't have anything to add about the game itself, but as someone who was in the arena (for part of the game), I was shocked at how disinterested the "fans" were, particularly in the pricey seats.
I went from Orlando to Miami to meet a friend for Game 3. We didn't have tickets because someone who looks a lot like me saw the ticket prices last Tuesday, and cleverly decided that seats for the Saturday game would become much cheaper once the Heat were down 2-0.
So, seats were crazy expensive, even once the game started, and even for bad seats. My friend and I decided to wait outside until good seats became available for just "too much," as opposed to "an obscene amount." It took until well into the second quarter before even two middle-aged lawyers could justify the outlay.
Finally, we gave in and got seats in the "South" zone, which is the VIP section that includes lounge access (which we cared nothing about). We were center court just a few rows behind the table with the TNT commentators.
A lot of people were still coming into the arena during the second quarter -- perhaps in part because of the early start -- but the fancy-schmancy area was decently full when we got there. The fans in Celtics gear were attentive to the game, but a large number of Heat "fans" were just chatting with each other and barely watching it. By the beginning of the third quarter maybe half the people in that section were gone, perhaps to the lounge (which did not have a view of the game). I think that the majority of those remaining were Celtics fans, even when the game was far from decided.
It's true that the asking prices for those seats were insane, and it may be that many of the occupants were just rich people there to be seen, or those provided playoff tickets as a non-Kendrick perq by companies that owned the season tickets. Even the nosebleed seats would be too expensive for a lot of younger fans who might be more enthusiastic about the game.
I know really good tickets are extremely expensive in all arenas, and don't necessarily go to the best fans. However, I've attended several Celtics games, including some that they lost, and I don't recall seeing people clear out like this. This experience reinforces my perception that the Heat has a weak fanbase, at least as represented at the games.