It’s kind of interesting and confusing that you need iCloud to back up your iTunes purchases, when keeping a tab of what you have bought for later re-download is a core function in any download service, just not iTunes.
Build Your Own iCloud – PCMag.com
As you get specifically the above for free, my guess is that iCloud stores a placeholder/reference rather than the content, which doesn’t take much space at all in comparison.
After all, iTunes has only one copy of each product, so why multiply that storage space on iCloud?