I like hard fouls and think the NBA calls too many flagrants these days (or makes them too severe - Turiaf's ejection in Game 4 of the Lakers series should have been a Flagrant 1 I thought, not a 2 and an ejection) but this is the equivalent of kicking a guy in an injured ankle.
Horry obviously saw an opportunity there, he clasped his hands together and leaned in to drive his elbow into West's lower back as he jumped up to deflect a pass. Horry has been in the league long enough, and has had enough incidents to know EXACTLY what he was doing. A hard foul, to me, is leveling a guy going up for a shot or screening a guy to the floor like KG did. I like hard fouls, and think they have a place in the game that has been unfairly restricted. Deliberately targeting an injured area on an opposing player who has been killing you, on the other hand, is just dirty.
And yes, the Spurs thing does come into play - they are the only team I can think of with multiple instances of deliberately trying to injure players (see Bowen kicking Stoudemire's heel out from under him on a dunk attempt, or the dozens of times he deliberately puts his foot under a descending jump shooter's to try and twist their ankle, or Horry against Nash last year, or Bowen kneeing Nash in the groin, etc, etc, ad infinitum). This makes this incident seem much less ambiguous to me, and I think I'm justified in doing so. This is the sort of stuff the NBA needs to crack down on, in my opinion, not just the heavy contact type of fouls. And the Spurs fans applauding causing an injury is just classless - I'd like to think Boston fans would not do the same but I might well be wrong (might depend on the player). To everyone saying this is a legit play or unintentional, please remember this if we play them in the Finals and Pierce just "happens" to get repeatedly hit in the back, or Bowen "accidentally" stands under Ray's feet on the way down 5 times a game.
PS. IndeedProceed, your picture link is 404'ed for me, can you post another?