There is a bit more going on. I don't know how easily you could jump into the market at this point. Shapeways benefited from being one of the first to offer a 3D printing service, so they didn't have too much competition. There was also a bit of an overlap with their early community and the community around Blender, so the userbase was able to grow quickly. They had some growing pains early on with delays in printing although it appears that they have worked through most of the issues at this point. It wouldn't be impossible to have similar success, but being the new guy in the market isn't always the easiest. The best bet of course is to not just join the market but expand it.