I completely agree, which is why I think there should exist a "Dota HD/Dota Remastered" (AKA Dota 2) for this exact reason.
Buuuut I think SC2 is a bad example. SC2 is actually probably an example of what Hobart is talking about (or, at least, it's somewhat similar to what I'm imagining in terms of scale of change). Dota 2 is practically a modern port of the original Dota while SCII has completely different units, strategies, etc. compared to Brood War. Blizzard has removed entire units while adding game-changing units and abilities, and they're planning to do even more with the following expansions.
It's a completely different metagame. In fact, to the layman, the divide between Brood War and SCII could seem at least as great as that between Dota and LoL.
This is actually why I'm also very interested in Blizzard Dota in addition to Dota 2. I know a lot of people here are going to be quick to dismiss BDota (and I have my own problems with it), but it'll be interesting/illuminating to see what changes/additions in BDota will work and which won't. Whether it be SCII, WoW, or what have you, Blizzard is not afraid of completely reworking a game to see if they can make it better,even if the prior metagame was balanced. It's risky and ballsy, and I respect the hell out of Blizzard for regularly trying these sorts of things.