I think your remark about pop being in decline is slightly inaccurate...to be quite honestly I am getting a bit pissed off about this, because I have read many news articles about 'pop' music being on the way out.
Everbody seems to forget that 'Britney' is still in the top 5 and thus maintaining a higher position and selling more albums than other rock, country, soul, rnb and rap albums.
I think coolguy16 got it spot on with his remark about there being a general decline in all cd music sales...
and what's this about Britney will survive?...she doesn't have a terminal illness.
She may not be doing as well as OIDIA but she is doing a hell of a lot better than a lot of other music genres!