White's N maneuvers are instructive.

I think many people would have been trying to hold on to the passed b pawn. My guess is that Smyslov decided that pawn would fall and he might as well convert to a modest material advantage.

So what was black's mistake? My guess is 36...fxg4, followed by 37...Bd3. If he had played 36...h6 and maintained the pawn at f5, white would not have broken through.>

Although I substantially disagree, I think this is an excellent comment because it is very thought–provoking. I would offer these observations: (1) After move 30, the position looks to me to be one in which White does not yet have a won game, but does have good winning chances primarily due to the superiority of his Bishop and White’s better prospects to activate his King utilizing Black’s weakness on the central dark squares; (2) Accordingly, it made perfect sense for White to continue playing (and would have done so even if the two opponents had been of a class comparable to one another); (3) if the position after move 30 had arisen, for example, in a game between Kramnik and Leko and been agreed drawn at that point, the kibitzers with howls of protest about "Drawnik" and "Drawko" would have been legion; and (4) finally and obviously, Smyslov had every reason to expect he would have good chances decisively to outplay a “mere” 2300 player in an endgame (even if the position at move 30 had been equal).