This is Lucasarts we're talking about. The ability to save some stuff back for the full game is too good to pass up for them, be it heroes, planets, units, that kind of thing. I bet the demo is only going to be the equivilent to a sneak preview, having only a fraction of the units etc on display. It just seems consistent knowing how Lucasarts deal with these things. To be honest I'm surprised there's a demo at all.