Luckily this has been true for Apple so far. But there is still the chance in the future that they stop supporting the DRM (either voluntarily or involuntarily).
Just look what happened to Microsoft's ironically named "PlaysForSure" DRM. They shut down the DRM servers in 2008 and made everyone's "purchased" content unplayable.
edit: I double-checked how Apple FairPlay DRM works to make sure I wasn't mistaken. But no, to play FairPlay DRMed content, you need to log in with iTunes which downloads your user decryption key. So if you got banned from Apple's services (credit card chargebacks, etc) then you can no longer log in to play your content, even if you have the media files. So you are only licensing it for as long as you agree to the terms of service, not buying it.
Right, so THIS aspect I totally agree with: If someone says "Buy", it must be possible for you to hand down a copy of that to play to your great-great-grandkids. That means it can't be turned off or lost because your account is cancelled; and shutting down DRM servers should require unlocking all DRM'd content first. Otherwise "Buy" really was a lie.
Just look what happened to Microsoft's ironically named "PlaysForSure" DRM. They shut down the DRM servers in 2008 and made everyone's "purchased" content unplayable.
edit: I double-checked how Apple FairPlay DRM works to make sure I wasn't mistaken. But no, to play FairPlay DRMed content, you need to log in with iTunes which downloads your user decryption key. So if you got banned from Apple's services (credit card chargebacks, etc) then you can no longer log in to play your content, even if you have the media files. So you are only licensing it for as long as you agree to the terms of service, not buying it.