Yes, The sale of singles is down hugly! In the Uk you only need to sell 30-60 thousand copes to get to number one, this compaired to 130,000 on average pre 2000.
However, the reason for singles is to show the buyer what the album has to offer, this can still be done through d/ls. An average 1M singles are sold per week compared to double that in album sales.
Here's a link about the UK record industry showing that it increased by 1.4% in 2005.
http://www.bpi.co.uk/index.asp?Page=new ... _966.shtml
Even where the 'problem' is at its worst in the US the sales of music is down 1.9% while legal d/ls has trippled to 6% of the total market. If legal d/l keep growing at this rate, soon (sorry my maths isn't good enough to give a estimate!) it will compensate for the loss in actuall record sales.
This is why i think people who say the music industry is on its arse are just scare mongering. It may have taken the 'big five' a while to react to d/l's in a way other them to sue them, but with sites like Itunes the industy is finally getting to grips with how to make the most out of a less then ideal situation.
( i just want to point out that there are so many different stats for this that its difficult to know which are bias and which are independent so my figures could well be wrong!!)