It's being used in more and more foods now. Off the top of my head -- I think Eagle Pack and Back to Basics have used pork in at least some of their products for a long time (as in many years). At least a couple of the Acana products have pork in them. Steve's Real Food has a pork based food. Several Science Diet products, including some of their "prescription" foods have pork in them. I suspect you'll start seeing it used more frequently as the demand increases more and more for "novel" protein products.
Trichinosis from raw or under cooked pork used to be a worry, as was the fat content of the cheaper cuts. But I think the idea that dogs and cats shouldn't be fed pork is like a lot of things--a little bit of solid reason (that can usually easily be overcome) mixed with a lot of unsubstantiated myth. There's also a theory that pork was shunned as a pet food ingredient for a long time because of propaganda from the beef industry.