I'd say the biggest issue isn't whether or not one has to get into the other stores – but how fast one has to get into them. With the eBook eBook, I was quite keen to make sure my store, Amazon, and B&N were all ready to go. Kobo will happen, as will the iBookstore… but it's much, much lower on my priority list.

Where this factors into something like Smashwords (or any other distributor) is the tradeoff you make with them. Is a 15% take of all channels worth the added exposure of the other channels? I'd argue it's not worth the time and energy to format to their specifications and to give up that degree of control. Others feel differently – but it's something that isn't being logically considered.

Or to put this in non-Smashwords-oriented terms: If your choice is between getting into another tiny eBook market or writing another page on your new story… write the damn story!