On irc dww was talking about. As I tested zip last year and it failed, I was curious if it worked today. It didn't...
This doesn't seem a big issue as every project is packed as .tar.gz on drupal.org. But apparantly we are going to add the possibility to download the project as a zip file. Every sane windows user will download a zip and not the tar.gz. Those people will complain cause the installation fails which leads to dissapointed (maybe new?) drupal users.
We have to fix this before drupal gets released, BUT I agree it's not critical.
Here is the error message as a starting point:
UpdaterException: Unable to determine the type of the source directory. in Updater::factory() (line 100 of ...\includes\updater.inc).