I don't necessarily agree with this. I think the reason why flat UI is having a moment is the same reason minimalism in general works. You get to remove anything things that are superfluous and focus on data/information. As awesome as spinning 3D globes and background rivets are, I prefer flat design when it comes to getting information.

I think it's best to try to get rid of unnecessary garbage in your UI, maybe that's the skeuomorphism, or maybe it's the amount buttons, images, content, etc. If done well, flat design is a usability win.