This is a common issue for all airlines. I can't tell you how many times I've been delayed, the GA tells me it's either mechanical or crew rest (or something similar that's under the airline's control). Later on, the story gets changed to weather so that the airline has no responsibility to its pax in terms of vouchers, etc.

There was something like a passenger bill or rights a few years back that noted something about telling the true reason for delays, but seems that this gets overlooked quite frequently. Not quite sure that there is any way to complain about this...don't think it's an issue that the FAA would be interested in, but I may be wrong.

It's very frustrating and I've called the airlines on it many times when it turns into something significant (bump, cancellation, etc). They told me that it was weather, I said it's not (helps if the weather is good that day ;-) and that I know it's related to mechanical (or whatever). I politely ask for what I'm entitled to (in terms of meal vouchers, etc) and have never been declined. That said, this changing story hasn't happened to me in quite some time.