The single domain license change occurred before Power CMS 2 was released.Power CMS 2 was released with the single domain license restriction in place.
The multiple domain license would be in effect for any version of Power CMS1 that you purchased.
Any version of Power CMS 2 that was purchased would fall under the Single Domain license though.
The Single domain license is applied to a single Live Domain, we do allow for installing on a second server for testing purposes.