Micro amps are perfectly capable of powering large cabs loud enough to induce vomiting. But most folks who use them use small/medium cab rigs because they're also looking to downsize their cabs. It's a choice and cetainly not a reflection on the ability of a micro to produce sound and lots of it in a big cab.
However, there is a difference between the micro amps and the big iron amps like the SVT 4 Pro. Just like there's a sonic difference between all-tube amps and traditional solid state and hybrid amps, there's a sonic difference between the micro format and the other two formats as well. Some folks will say that these differences are design choices and not based on type of amp. I say they're wrong
I've yet to play a micro that has either the hard attack of trad solid state or the 3-dimensionality of a full-on tube amp. Don't get me wrong...I like micros a lot. They aren't as tight as trad solid state, and in some ways that reminds me of a tube amp being pushed slightly hard and I like it. And they're super light and easy to carry, which is awesome for gigs with tough load-ins. But they are most definitely different from the other two previously existing types of amps.