The lack of speakers isn't a big deal to me. I mean, the built in speaker is solid enough, and it looks to me like the dock would only cove half of the SGS, so you could plug in headphones or your own speakers.
My guess about the lack of speakers is that the horrible evil iPhone plug has contacts for headphones/speakers there. You could build one for the SGS, but you'd have to have a truly separate 3.5mm jack, and in horizontal orientation you'd have to be very careful sliding it in and out to avoid breaking it.
Also, this dock is very small, and so having anything on board would seem unlikely. I expect there will be some 3rd party docks coming soon enough to cover what you want.