OK - finally read the whole thread. Ashlee isn't the most talented artist to sign a major label deal but quite honestly she isn't any worse than a good half of the artists being played on Top 40 radio and selling lots of CDs. This isn't so much a statement about her as it is a statement about how little the record buying public cares about great singers, great songwriters and great musicians (and they don't all have to be the same). No question a lot of famous singers use a lot or all taped vocals when performing "live".
The blame really lies with modern recording technology and the ability to pitch shift vocals (and other instruments) so easily (ProTools and the like). Consequently the ability to sing in tune - particularly since you don't have to sing live either - is not particularly relevant for a lot of major label promoters, etc...
Anyway, I have lots of other thoughts about various flaws in the music business but I'm actually really surprised this hasn't happened more frequently.
It did remind me of the time Joe Jackson played on SNL and had a big alarm clock on his piano and played "Soul Kiss" - a song which ran around 4.5 - 5 minutes. During the guitar solo and at 3.5 minutes he pulls out a whistle - slaps the alarm clock and stops the band calling out "that's it, our allotted time is up!"