The problem with you deciding that Blizzard is making this change out of pure laziness is that this POV depends on Blizzard wanting DKs to be "just like every other class" when death knights -aren't- like every other class and, even with this change, won't be. Is Blizzard making this change because it'll make DKs easier to design? Yes, but that's not a value judgement. I don't see any point in them sticking with the "every tree can tank" experiment at the expense of making the class better and more fun to play.

While every tree may be balanced now, in Cataclysm everything will change so drastically that, just by way of game mechanics, that probably won't be the case. Basic things that we take for granted now are going away completely. The talent trees are getting a complete overhaul; how could things possibly stay as they are? Blizzard is looking ahead, realizing that the cost of maintaining the gimmick outweighs the benefits to the class, and going with the most efficient route. Your personal disappointment is talking when you say that this isn't about the players and all about laziness on Blizzard's part, since anyone speaking from an objective point of view can see that they work very, very hard on getting this shit right. They don't always succeed, but the fact that they're on the forums daily talking about it and asking for feedback and actually, constantly balancing instead of letting classes languish at near-unplayable states for years the way some companies do should tell you something.