Much has been said here about the disinformation pursued by the RIAA to convince each and everyone that illegal downloads are the sole reason behind poor sales. Turns out its British counterpart is up to the same standard along with its sidekick, the Ministry of Intellectual Property. Witness these two Guardian articles.
The first one discusses a claim that the revenue lost due to file sharing amounts to a tenth of GDP. It turns out numbers were off by a decimal. And then still overinflated by assuming each download had an opportunity cost of £25. And let us forget an argument about price elasticity and the difference between a price of £25 and £0.
The second one shows that the reason music sales went down is maybe due to the fact that there are better alternatives to music, like computer games and DVDs. Sales numbers would certainly be consistent with that.
Third, market saturation
. As you acquire material goods you begin to run into problems, such as storage space and time available. In fact, assuming that you have established a "good" library you may also reduce buying new content because it is "duplicative" to what you already have. (How many version of the movie Titanic would you buy?)
To expand a bit on the second point, a person has only so much time in a 24 hour day - so if presented with many entertainment alternatives - decisions have to be made concerning what product a person will invest their time in. Do I buy a DVD or buy a CD for tonight's entertainment? Obviously the preceding example is flawed, but my rationale is to point out that you will only buy so much before cutting yourself off. I will even venture that as we age, we buy less and less new content.
In my case, there have been several DVD sets where I have only bought one of the three DVDs available. I would like to eventually buy the whole set, but I have a storage problem and I also wonder whether I would really watch the ones that I didn't buy. My library is "saturated".