This is standard. YouTube used to remove films where music was used which did not belong to the poster, but now they have a new method- they email you so you know they are on to you. Then they either cover your film in adverts, which is how the music gets paid for, or they stop the video being shown in certain countries. This is all dependant on the publishing contract which the composer of the music has. One of my films uses a tiny bit of "Time" by the Alan Parsons project and as a result, there are now adverts on that film, and also it is not available in Germany for some reason!
Basically, you can only put up a video which you own all the rights to. ie- your own compositions. If you put up music belonging to anyone else, the composer needs to get paid for it. Since you aren't likely to pay, YouTube instead 'pay' the artist (PRS/MCPS) from money generated from adverts which are put on your video. Seems fair to me- Lloyd Cole gets paid, your video stays up, everyone's happy!