One popular theory is that, like newspapers, record labels have lost pricing power because they can no longer bundle (in particular, putting one good song per album and charging $13 is a thing of the past). The RIAA (implicitly) dismisses this line of reasoning in the associated notes:
If digital singles are converted into an album equivalent (divided by ten) and added to both CDs and digital albums, the overall album unit decline in 2008 was 14 percent (635 million to 545 million).See ... less overall units means people must be stealing music, because their demand for quality product has not decreased! Quick, pass some laws ...
However we have established that an album is not equivalent to ten good singles. Let's be generous and say an album is equivalent to 3 good singles. In this case the picture is rosier:
Viewed this way demand for music is about the same, with the difference being attributable to the economic climate. Furthermore, if two singles are considered equivalent to one good album, then demand has actually gone up.
Finally, it's amusing to note that a greatest hits album from the early 1970s is the 2nd highest selling album of all time, selling 48 million copies and therefore roughly valued at $500 million dollars. Clearly the media consumer had less capabilities in the past if they were willing to collectively pay $500 million for someone to assemble a set of previously released tracks into a single physical format.