They must've some big reserve to be able to act as a interest bearing wallet, but that could only be profitable for us if we were to deposit large amounts and not a few dollars worth of Bitcoin.
Deep pockets? Absolutely! See here >>>
https://bitcointalk.org/index.php?topic=1922196.msg19104276#msg19104276Would you keep your paper money in other peoples wallet? I don't think so.
If you keep your "paper money" in a bank, it's sitting in an online wallet. There are no private keys for paper money, only the paper money...so if it's not literally in your possession, you don't own it.
What's the fee for withdrawing, though? Or is that free?
I don't have this information at this moment, but I can get back to you. If you want to test it though, proceed through the process and screenshot what appears, what you experience.