I think the cinematics etc. just make it seem like the proportions are a lot different. That was pretty much my first point of confusion when I started playing - I felt like most things ought to be a lot bigger with the exception of the Rook (who was already collossal and now even larger).
I think the scale is staying pretty much as is, though. The creeps are meant to be miniscule and easy to murder en-masse (as opposed to most RTS and the way that a certain unmentionable game works). I'm over it, it's not such a big deal, although I would like it if creeps weren't so easy to ignore, like you could actually get killed by them if you're not paying attention or playing well early on and even later on.
To directly answer your question: No, I don't believe you can change the scale of the units in-game, although if modding becomes available that will probably be possible.
