When Apple announced iCloud to replace their MobileMe service they gave MobileMe extra free storage on iCloud. iCloudl comes with 5GB of storage for free.
Apple gave old MobileMe users a total of 20GB of storage for free, that has now ended, and the storage has now been set back to the free 5GB of storage.
As you can see from the photo above, I just received this email from Apple confirming that my free iClould storage has now ended. If you want additional iCloud storage above the free 5GB this can be purchased at an additional cost.