Some iTunes Eligible Content that you previously purchased
May not be available for subsequent download at any given time,
And Apple shall have no liability to you in such event.

from Apple (Ft. Hella Apple Lawyers) – ITunes Terms of Service 3 on Rap Genius

You bought a song on iTunes. Then you lost your iPod and macbook. You buy a new iPod and macbook and want to put that song back on it. But now we don’t sell that song? But you bought it, don’t you own it?

No.

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