There is no doubt in my mind that there ARE successful companies that make exclusively Mac software. But unfortunately, I cannot provide you with links to all the dead companies that did, or wanted to be successful Mac-only software shops.

Also, I have searched for a Mac shop all of my career. I'm sitting here typing this at work on my Windows box, with Visual Studio open to my C# code in the background window. Its a dream that I wish I could persue, but it, like my dream of being a rock star, is dead.