It's possible it's more the person's running the PA's fault than some kind of ego trip from the guitarists
+1, Based on the picture you provide, the amp appears to be mic'ed (see the small boom on the left) so the fault is the soundguy.
I realize that at some small gigs, the amp is part of the overall amplification, but for larger gigs, the amp exists for the musician to hear, and for the Soundguy to mic so the audience gets a good sound from the PA. Tilting your amp back to face you, allows you to play at even lower volumes onstage. It also allows you to play with feedback effects and mess with the amp without facing away from the audience.
I don't ever face the amp away from the audience, but...
I sometimes find ways to tilt my speaker (4x10, or 2x10) up at me so I can get a better tone, I do this..
-When I'm in a club so small that the audience is going to hear it no matter how I face it.
-When I'm on a gig, where most of the sound is in the PA, but I can't stand far enough away for the sound to get to my ears well.
My 2x10 cab even has a small handle on the bottom designed to pop down as a tiltback.