As a personal anecdote, I have never felt anything that I was inclined to call "willpower depletion". As a teenager, I decided that "willpower" was just a loaded term/metaphor for dynamic consistency, and that calling it "willpower" was harmful to the way people thought about themselves as agents. I decided that other people's feeling of "willpower depletion" was nothing more than sensing oneself in transition from one value system to another.
But claims that the theorized "executive system", a cognitive system whose function is almost by definition to maintain dynamic consistency, was seated in the prefrontal cortex and needed more glucose than other brain functions, made me consider that maybe "willpower" is in fact an appropriate term... but I still never actually felt anything like a "depleting resource", which I found confusing.
So I'll be less confused again if the belief dependency you mention is correct, and causal. In any case, I hope it is, so that people can achieve better dynamic consistency by not thinking of it as "expendable". I'm at least one example consistent with that theory.
With respect, I've always found the dynamic inconsistency explanation silly. Such an analysis feels like one is forcing, in the face of contradictory evidence, to model human beings as rational agents. In other words, you look at a person's behavior, realize that it doesn't follow a time-invariant utility function, and say "Aha! Their utility function just varies with time, in a manner leading to a temporal conflict of interests!" But given sufficient flexibility in utility function, you can model any behavior as that of a utility-maximizing ...
Stanford Report has a university public press release about a recent paper [subscription required] in Psychological Science. The paper is available for free from a website of one of the authors.
The gist is that they find evidence against the (currently fashionable) hypothesis that willpower is an expendable resource. Here is the leader:
(HT: Brashman, as posted on HackerNews.)