I'll admit it was a poorly officiated game overall (for both teams), but it was especially damaging to the Spurs because of the timing and impact of the calls - like when 2 obvious fouls by Dirk (and they were pretty obvious - not really judgment calls like block/charge) in the first half (when he had only 1 foul at the time) went uncalled and then Duncan ends up getting his 3rd at a pivotal point in the second quarter. Then Devin Harris jumps into Ginobili with his elbow (Ginobili required stiches), but it's called a block and Harris gets a 3-pt play out of it. Also, the Spurs are making a small comeback, but the Mavs are on the break, and then Brent Barry gets called for the 2nd worst block call of the playoffs (I'm still partial to the Kobe over Nash dunk because of my fandom) - a huge momentum-shift possibility for the Spurs that goes in favor of the Mavs. (And Barry was planted at least a second before Howard got there/went up - a really bad call by Javie, which no doubt intensified the "Javie Sucks!" chant from a relatively knowledgeable and fair SA fan-base.)
In all honesty, it seemed as if the refs had a quick whistle all night long (2 quick techs on Pop and Avery; Van Exel gets ejected), but the most extreme example was the inadvertant whistle play where the ref jumped the gun thinking Ginobili (who is a smart player and was just trying to shield off the Mavs) was going to touch the ball and then didn't. The call forced a timeout and jumpball, which also affected the Spurs momentum after just getting a stop at the other end. I mean, I'm in no way a Spurs fan right now (not until the Suns are eliminated), but I just don't like seeing a team that is struggling in a game have to endure officiating that impacts their momentum in such a way, especially when the Mavs seemed to have an answer at the other end for every Spurs score - they needed every break to go their way and it seems like these plays and calls just took the life out of them.