I didn't say Dearmau5 was great, or anything... but listening to some other guys in that genre, he made me pay attention with a few things i found good. I don't know his whole work, because most of it is boring, like with most music in the electro scene. It's all too repetitive and overdone.
Song structure in 99% of these songs is the same, you don't have to be a good songwriter or anything, because the mold is already there (even if you write a classical symphony you have a previously conceived mold). Regarding melody, here comes the part where the arrangement overcomes the actual song... voice leading in harmony is all for this song, there's no real melody (most dubstep doesn't have proper melodies, it just has cool beats and well crafted sounds). Melody in this song comes from the voices in the different chords and how they link, the arrangement the pianist does makes a few choices that are great, he made focus in a few lines that work great, which are not so easy to listen in the actual song.
I don't consider neither skrillex or deamau5 good songwriters... actually, it's hard for me to find a producer that is a good songwriter. They have cool moments, and some good ideas, but it's not consistent, and one good song in ten average ones, doesn't make you a good songwriter.