I'm not all that impressed because it's all about quality, balance, and yes... writing, when it comes to a good RTS experience, not just being able to throw out crazy numbers of units. While I guess some people really liked it, I could never get my mind around the concepts and why the factions were fighting (and the whole idea of one suit building an army and that resolving an entire war, when you'd think each side would have thousands upon thousands of nanite-constucting battle suits, but well... yeah, best not ponder that) in say "Supreme Commander" which as it's selling point was pushing the number of units you could crank out and how it had carefully balanced sea, air, and land components with one faction being able to morph it's units to more than one element as a special ability if I remember.
The point I'm making is that while I suppose the technological achievement is impressive, I think things have remained on a smaller scale largely because it's both easier to control, and to ensure the quality of the experience. Blizzard could have say moved to a larger scale, say Supreme-Commander-like but I don't think it would have had the same quality, and I'd imagine they do also, because they didn't do it at the moment.
At any rate if you want to impress me, come up with a system where you can crank out that many units and provide me with an interface where I feel like I can actually control that many and remain more or less in command of my entire battle. Simply churning out unprecedented numbers of AI bots that might at best wind up following a patrol pattern in of itself doesn't sell me.