Hi Rob--
my impression is that itunes is set up to allow free downloads of apps you have purchased in the past--
but the rules seem to be different for music.
here is the response i got recently after i was charged twice for a song i clicked on twice within a minute or two:
Dear Jonathan,
Thanks for contacting the iTunes Store. My name is Leah, and I'll be responsible for your inquiry today. I understand that you were billed twice for a song that you purchased. I can certainly appreciate how eager you must be to have this resolved.
Jonathan, I have reversed the charge for the duplicate purchase, which I understand was unintentional. You will see a credit of $1.08, in three to five business days. The credit should be posted to the credit card that appears on the receipt for that purchase.
Please note that this is a one-time exception, as the iTunes Store Terms and Conditions state that all sales are final.
In the unlikely event that you receive a download error in the future, please remember that it is not necessary to repurchase items when downloads are interrupted, because the items should still be in your account, waiting to be downloaded. To learn more, follow the steps in this article:
How to resume interrupted iTunes Store downloads
http://support.apple.com/kb/HT1725
Jonathan, the iTunes Store provides a warning message that asks if you are sure that you want to buy an item. This warning can be turned off. If you would like to make sure that this warning is on, you can reset the warnings in the iTunes Store by following the instructions in this article:
Resetting iTunes Store warnings
http://support.apple.com/kb/HT1734
Resetting iPod and iPhone warnings
http://support.apple.com/kb/HT2527
Jonathan, please let me know if you have any other questions or concerns about this issue. I'll be more than happy to assist you with whatever you need. Thank you for the chance to improve your iTunes experience.
Sincerely,
Leah
iTunes Store Customer Support
----------------Jonathan