Indeed. There is no difference between Magic in Warcraft and Psionics in Starcraft. Everything you can do with one you can do with the other.
You might be inclined to call Starcraft Science Fantasy rather than Science Fiction, but then so would D&D be unless you reskin everything.
Incorrect. I clearly said that this was only due to Blizzard using the same engine for all their RTSes.
In their RPs like WOW and Diablo 3 (as reminded by @Aldarc ), classes use different systems to more accurately display differences in their abilities.