It's a little confusing. The music you purchased from iTunes isn't stored in your personal iCloud account. It's stored in the iTunes store, and (in most countries) can be redownloaded again for free should you need to. Apple calls this "iTunes in the Cloud". The process for doing this is explained here: http://support.apple.com/kb/ht2519. This article shows the countries where iTunes in the Cloud downloads are available for different types of data: http://support.apple.com/kb/HT5085.
The document you were reading says "You get unlimited free storage for...Purchased music, movies, TV shows, apps, and books". This was referring to iTunes in the Cloud, not your personal iCloud account.