Playing Devil's Advocate here...
Aren't there a lot of older bands that don't have the voice that they used to and other older bands that detune as a result of that? Yet it seems like the band that gets brought up most other times (Ozzy/Sabbath excluded for obvious reasons) would be Metallica. Is it just because they are pretty much the most notable and successful metal band going and the target on them is just that much bigger? Is it from the hostility that most still have for some of the more recent releases (St. Anger & Lulu) and its just easier to trash them?
Having seen videos of live stuff from Black Album and before I'd definitely agree they don't seem to have the fire and anger onstage like they used to, don't think anybody would deny that. But honestly, when you are rich enough where you can almost print your own $ type of rich, then yea I'm not surprised. Everybody's in their 50s now and could retire now and live off of whatever $ they had before, how can you really come out on stage looking pissed off and angry and not come off phony?