Can I still install a fresh copy of Win 10 Insider Preview?

The other thing is, if the Insider preview is basically free, why would anyone splash out hundreds for the retail version? Who cares about a slight watermark.

Because insider previews expire and some people, like me, don't want to have to keep loading new builds of Windows just to be able to keep using it. Also insider previews are not as well tested as the release versions and will contain more bugs.

Alright, cool.