UK =/= Europe. BTW has been an internationally successful song, regardless of where it charted.
But that's neither here nor there, EMA's are fan voted awards for the most part (Best Video isn't, which she won also) so it's obvious that Gaga and Bieber would triumph considering how massive and active their fanbases are (same goes for that Korean boyband that won). Especially compared to the likes of Adele who doesn't have that.
Plus, it's an award show after all. They like to reward big artists for showing up. There were reports of Gaga getting something like 60 million votes, beating Bieber in the "Best Fan" category (which was not televised) but somehow was outvoted by Bieber in "Best Pop" (which was). Funny that. Katy Perry won "Best Live" but in no way could she have outvoted Gaga. She was there though and has hosted a few times, so of course she won something in the televised show.
Adele was unlikely to shine in any of these award shows, it's the Grammy's and Brit's that she'll dominate.