Then I would imagine the official site would have a downloadable binary already compiled. Github isn't really a place for getting compiled binaries, it's for collaboration and source control. I've never gone to a repository with the intent of being able to download compiled anything, chances are if you're apt enough getting to the repository you'd already know to expect this.
The author or vendor should be supplying a compiled binary for download in my opinion somewhere else like their website or even via Bittorrent.
For a lot of projects the gh-pages 'is' the official website. Smaller projects have never (until now) needed another location to host a full project, you may disagree that github aims to be a place to host open source projects but gh-pages, a hosted wiki and issue tracker suggests otherwise.
I don't know about this stuff, so ask in earnest: couldn't such smaller projects upload their compiled installers to some free app hosting service, and link to that from their github site pages?
But Github has been moving more and more to be the site for a project, that's what Github Pages is explicitly for. It was nice to have everything under one place, with one account system. Not unrecoverable, but to me this was a regrettable decision for them to make.
Maybe the change is to combat those who have been leeching off of Github for free bandwidth. If you're serious about your project and you're consuming enough bandwidth to worry about a big S3 bill, you're probably big enough to be able to afford to pay for bandwidth. S3 is cheap and dead easy to use.
The author or vendor should be supplying a compiled binary for download in my opinion somewhere else like their website or even via Bittorrent.