I'm not sure when it started exactly, just that it's not unique to the Bush administration. I think it is more prevalent now, but I think it's more a function of the number of news outlets.
Let me be clear that I agree that all outlets should cover these things; it would be harder for people to simply tune it all out, and they might actually learn something.
Fair enough. I'm not so sure I give the networks such benefit of the doubt, but I of course can't prove any suspicions based on my observations over the years. :)