this stuff is interesting... I think you also have to think of CD sells kinda like money...
Everything goes up in value as prices go up : / So $100 10 years ago was considered around ,what, maybe $200-300... Except CD's do the opposite
if an artist sells 500. copies now it would be considered alot more for back 'in the day' don't you think? So many new variables plague the music industry, like bootleg copies, illegal downloads, and now you can usually download an entire album for around 9-12 dollars? (at least in USA you can... it's probably a little more expensive in Japan but everything there is a little more expensive

)
So with CD's becoming obsolete soon fans are starting to decrease in buying CD's... Why get a destroyable and scratchable CD for 10-20 dollars when you can get a nearly undestryoable mp3 for .99 cents?
So thats why I think saying that Ayu doesn't sell as much as she used to isn't necessarily due to her 'falling' off her pedastool... but just the decline in record companies sales period! So adding a DVD to the CD helps ALOT if you think about it... Because you can download the videos online but the quality of DVD's are usually FAR much better and take up a small space on your shelf instead of a large one on your harddrive.