That xbox took forever to save for, so voiding the warranty wasn't an option. Luckily, the ole hairdryer defeated the tamper evident destruction of the sticker.
I love things like that. Microsoft pays for manufacturing of a security sticker to prevent tampering. On a device that runs a hypervisor (wild at the time) to prevent tampering.
And some dude on the internet realizes that you can just heat it up with a hair dryer and carefully peel it back with tweezers, than flash firmware to your DVD drive that reports "yep, this is an official Xbox 360 disk" to the locked-down-and-totally-secure OS.
Companies can only void the warranty on specific items that you damage. As long as you don't damage anything when opening up electronics, ask them to put in writing why they are voiding your warranty (chances are they'll "help you just this one time" instead).
The FTC is finally cracking down on companies that use such warnings.
(Magnuson-Moss Warranty Act - same law that lets you or third parties do work on your vehicles without voiding the manufacturer warranty.)
Considering the nature of hard drives, I think that would fall under damage caused by opening.
My understanding is that they are not in a vacuum, but they are super-clean. The air/gas inside is an important part by preventing the read/write head from touching the platters as they rotate. If a consumer opens it up, then dust is introduced which will cause problems.