Apple really has done a Microsoft in creating an application platform that will lock in customers for years. There are several apps that I would have a tough time giving up at this point.
I was making a similar choice, and ended up making the investment to go with the iPhone. The benefit has been that I really like the Mac - this is my first, and developing has been a lot of fun. I'm not looking to sell to the masses though, I am writing applications that support businesses with mobile content. Android would be my second choice, and I wouldn't even consider WM or Symbian.