Putting the belay device into the rope tie-in rather than the belay loop is common practice in the UK. Here is a link to a discussion about pros and cons: www.ukclimbing.com/articles/page.php?id=1129
. I first learned about it many years ago from Chris Harmston, then the BD engineer and one of the most authoritative voices on climbing safety procedures I've encountered, and since then, I have always belayed this way. It has nothing to do with mistrusting or sparing the belay loop. A factor-2 directly onto the belay loop does, however, put all kinds of opposing forces on the harness which the device on the rope tie-in eliminates.