I don't see how it was a Megaton, Portal 2 was going to be released for PS3 like Portal 1 was. Just because of some negative PR stuff Gabe Newell said of the PS3 it is a Megaton?
Portal 1 was a pretty popular game but it was bundled with other amazing games, this is not a proven franchise yet.
Don't compare this to real megatons like Final Fantasy 13 on xbox or 2004 Zelda presentation.