Half a loser is better than one

Continuing my series on beginner/intermediate mistakes, I'm often surprised at how people end up pitching, not losers, but half-losers or even, in some situations, actual winners. Here's a hand I watched recently on BBO played by someone who I know to be a good player.

Dealer: S Vul: Both	North ♠ Q ♥ K9874 ♦ 654 ♣ AQ63
West ♠ 9432 ♥AQJ652 ♦ J8 ♣ 9		East ♠ 75 ♥ T ♦ KQT72 ♣ T7542
	South ♠ AKJT86 ♥ 3 ♦ A93 ♣ KJ8
Bidding:	S W N E 1♠ 2♥ P P 3♠ P 4♠ P P P	HTML Bridge Hand Layout Creator

North was hoping for a reopening double, but when 3♠ came around, was happy to raise to game. The opening lead was ♣9, won in hand. Trumps were drawn without having to cross to dummy.
At this point, declarer ran the clubs, pitching the losing heart, making 11 tricks after giving up the inevitable two diamonds.

What's wrong with that, you might ask? +650 was indeed the par result. But double-dummy defense starts with an unlikely diamond lead, knocking out the stopper there prematurely. On an the ♥A lead, of course, every declarer will make 12 tricks. Why did this declarer make only 11 (like most declarers in this contract)? I don't know what goes on these thought processes. But here's the way it should go:

After the actual lead, there are three losers, one of which can be pitched on the long club. But these three losers were not created equal. The heart "loser" is, in fact, only half a loser--because the ♦A hasn't been knocked out yet. And, given the actual auction, with West making a vulnerable 2♥ overcall, that heart loser is really about a 90% winner. So, unless the opening leader hits on the magic diamond lead, the 6♠ is practically cold.