I think some people are mistaking tilt for movement. There should be no appreciable difference between a secured HDD laying flat and one at an angle. So long as the drive isn't shifting about you should be able to have it sit at a 90-degree angle without a problem.
I did have a similar idea for a PC case design. The goal, as they sort of mention, is to better facilitate natural fluid dynamics - cool air falls, warm air rises. Angling the case upwards would, in theory, coalesce the warm air to the back of the case with the exhaust fan to more rapidly expel it from the case. This could easily backfire, however, since that likely also means building up heat around your CPU, volt. reg., and/or northbridge area. It is certainly an interesting idea worth experimenting with.