I think people are talking about different things here. Installing software(applications) from maemo.nokia.com or Extras repository obviously shouldn't void the warranty and neither should flashing it with official firmware to unbrick it. But if I try to install Android(also software) on the device bricking it in the process I don't expect Nokia to just send me a new one under warranty. I also don't expect the computer manufacturer to replace or fix my computer if something goes wrong with for example linux installation.