I think it's hard to argue that the source material has not been stretched here, you have single throwaway lines that translate to long ass scenes in The Hobbit.This assertion can only be made after all three movies are released. Then one can objectively look at the final product and say "yes, the same could have been delivered in 1/3 the time." I'm not saying the argument is wrong, only that, at this point, there's not enough to go on to really support it (aside from conjecture and claims from one side vs conjecture and claims from the other).
If you ask me, The Hobbit suffered greatly from that stretching of the source material, that being said, I agree that it's perfectly possible that we'll get two brilliant films next which may make that decision worthwhile, but so far, at least to me, it looks like a financial decision more than an artistic one.