M. Louisa Locke has a well-thought-out blog post about why she's continuing to make her book exclusive with Amazon. She's not saying it's the right decision for you, or will always be the right decisions for her--just that it's working well for her now. It's a more nuanced view of short-term and long-term thinking than Dean Wesley Smith's.
One thing she talks about is risk, and how it is unavoidable:
[A]lmost any action an author takes in the midst of the rapid changes within the publishing industry can be characterized as short-term. Putting your ebooks in the Barnes and Noble Nook store, given the effect of the Department of Justice decision on agency pricing, might turn out to be a short-term strategy if this corporation goes under. Concentrating on building relationships with bookstores to get them to carry your print on demand books (a strategy that...Smith is currently advocating) may be a very short-term strategy if those bookstores go under in the next 2-3 years.
And we've just seen how unavoidable risk is with Boyd Morrison. He's a successful self-published writer who got a contract with Simon & Schuster. And then they canceled his contract. What does that mean? Remember that fancy advance a writer is supposed to live off of as he writes his book? Morrison has to pay it back. (ETA: OK, it turns out that he may not. Hopefully he won't.)