Rather then speculating Arstechnica asked the Apple reps whether these news apps will work on the original iPad and the answer is yes.
'Apple representatives also confirmed ... that the new apps (iMovie and GarageBand) will work on the original iPad as well. "Obviously you won't be able to import video to iMovie in real time on the original iPad," one rep told us, "but you'll be able to do that through the USB camera kit. Probably."'
How useable iMovie will be is another question.