I applied (and got in) to Svbtle because of two things: exclusivity and the interface. Svbtle at least attempts to have only high quality writers there, and it was made clear that sometimes, if posts were of low quality, they'd be asked to be revised. There was also talk of helping Svbtle members with their writing through things like copyediting. I haven't heard of any of those things happening yet, but I can tell you that (generally) I try to keep Svbtle much higher quality as a result. I still maintain a personal blog where I put shorter/news kinds of things, but bigger, more in-depth essays go to Svbtle.
The interface is also really nice. It's good enough that I actually write in-browser, rather than writing in Vim and copying it over.
Oh, and also: I suck real hard at design, and I'm sick of maintaining Yet Another Blog Platform/design. I really like the look and feel of Svbtle. My personal blog is basically just Skeleton default with a few small modifications: http://blog.steveklabnik.com/archive
