Unfortunately BloomingLotus, advertising is just about the only thing that keeps social services like these alive. Just look at Facebook and Google, both rely solely on their advertising programs to keep their monster-of-a-service online.
In order for DeviantArt to retain it's art community and stay online, they must have these advertisements. But don't wrongfully assume that being "commercial" means the owners will stop caring about its community. It's actually quite amazing how DeviantArt still has that friendly community aspect.