I think BulletMagnet has hit it pretty spot on. But I think updates will be distributed in an automated fashion over some sort of digital distribution system. Possibly by relaying their binary contents across a world spanning interconnected transmission system composed of millions of computers. I think there are some examples of this sort of thing out there somewhere.
Sidestepping the snark above, the first alpha release will probably be several hundred megs to a gig or so worth of textures and content and game and stuff, and then the size of the updates will probably vary wildly in size, from 30 kB worth of "unit balance changes" to a few hundred megs of "New feature: Naval units!" to multiple gigs of "Hang on, Herp Derp uploaded the low-res textures; here's the UBER HIGH-DEF textures for ya!". As for schedule, there's probably going to be very little in the way of schedule from our point of view, but they say internally they're using an iterative/scrum development format (where you make smaller changes and keep improving over multiple releases, rather than coming out with one giant release), so I'd anticipate seeing new updates on a one-week,two-week or three-week basis. There will be some days with two releases as they quickly hotfix bugs, or just a few days between releases, or maybe they'll take a 3 week long cycle to get some major feature like orbital units or galactic war out the door. And yeah, as others have said, online distribution means you just download the new update when it's ready. Also, Uber, can you make (most) updates optional? Sometimes you just want to show a friend the game or you want to play right now and getting hit with "Now downloading 1 gig over your parent's slow DSL line!" is lame. I understand the need to nag people to upgrade so you get new things tested by the crowd, and that there are some hotfixes that just MUST be pushed to the public, but I think many people would appreciate it.
