Blizzard is pretty strict with the anti-cheating checks, which may be part of this. It's also very annoying that you can't run Diablo 3 on OS X if you have Filevault enabled, for example.
"This error is caused when FileVault options are enabled, or if a volume is formatted as case-sensitive. These options are not supported for installation."
"If FileVault is enabled, then Diablo III will not install."