Yep, if you buy Lion once, and say your hard drive crashes, you need to make a new iTunes account with a new credit card because you can't re-download Lion, and the installer deletes itself.
I made SURE that Time Machine made a backup of my Applications folder before installing Lion, and I'm 100% sure that the Lion Installer was backed up. Now it's not there if I go back to the day I installed Lion. I can't believe it actually deletes the installer from your backup as well! It's ridiculous. You can only install the OS ONCE, and then your only hope is your recovery partition. If that fails, buy a new computer or make a new bank account!
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If you had read any of the numerous threads on creating a Lion install CD, you wouldn't be worrying about this. That's how I installed Lion in my MBP at work. Of course, if I really wanted to download it again, I could do do so.