I'd pay extra for that, I (we all) have a bunch of personal sites, landing pages, marketing sites and tiny side projects that'd love to not have to deal with hosting – I think they'd make a killing, but also think must be in the works.
Github builds tools for developers. Atom, chat (abandoned), Pages, Gists, and github.com all fit within this. They tie into how teams operate. Serving JS is tangentially related — certainly something a web developer does — but not really core to their mission.
I think of this more as a convenience feature for their existing business that adds value. They use this instead of the "project page" design that the other code sites used, and it gives their users more control over the presentation. Which is awesome, and feeds into my conspiracy to get everybody to know and use HTML for presentation. :)