Docking with the ISS is like going where hundreds have gone before. This is the perfect place for a private business to go. The trail is blazed the risk factors known.
Getting to Mars with people is a whole 'nother thing. I hope he can do it, but I think it will take a lot longer and require a lot more ground work than some people think. I don't doubt he is aware of it, but I do think he's generated a fan boy base that isn't. Because another thing he has said is he wants to go there with NASA. Therefore, his estimates of getting there in 10-15 years if things go well include going there with NASA. If he can't get NASA to help I think it is easy to assume it'll take a bit longer.
Historically it has been governments that have sent out the trail blazers. Private businesses that can't estimate the costs and risks don't bother. They wait until the government has blazed the trail and then follow (East India company for example).
Poke around Youtube for Neil deGrass Tyson for an expansion on that last point. He puts it together very well. And while you're at it, sign the penny4NASA.org petition so NASA has the money go to Mars with Elon.