Blockbuster films usually have a bunch more sound effects, which is why they sweep the category. There's more to create and put together for, say, Star Wars than Juno.
I don't know, sound design is still a pretty complicated area. There's probably more work to be done in a blockbuster than an indy film (with bigger and better machines, though), but it's the end result what's important, right? As long as the sound serves the purpose it's supposed to serve, whatever that may be, I think the achievement is the same. The category is called "sound editing", not "sound effects", so it's kinda silly that it comes down to that.
Besides, I think indy directors care more about using sound editing in creative ways, you can tell some of them put a lot of thought into it. I remember the sound editing in Pi was really good and played a big part in creating the claustrophobic atmosphere the movie has. And David Lynch! I'd say 40% of the creepiness in his films is thanks to the treatment in sound. Has he ever won an Oscar for that? I can't be arsed to check, but I bet he's lost to big movies every time. Why? Because they need to say "8 Oscars" in the cover.
