It's hard to compete with the IBM's of the world on R&D or technical accomplishment. It's a bit easier to compete on the fronts of price and expertise for a particular customer. Means you need some serious exposure to retail systems, but there are a bunch of startups still reaching into this field - though it was a much more popular field when PC's first started appearing as I saw lots of garage operations trying to break into retail (a guy I worked with on a liquor store system POS comes to mind, as well as some video store stuff with my sister).

Just because one of the big guys has done it, that may just indicate it is ripe for competition. Hell, that's how a lot of open source projects get started. :-)