It's not mentioned in the specs, but there may be an additional mask relief between pad and printed mask. This ensures that the copper pads will not be covered with mask. If the mask relief is 2mil, the minimum required space between the copper pads would be 2+3+2=7mil, otherwise the mask would be rejected.
On a few boards that I have received so far, the mounting holes and mousebite holes were non-plated. In the gerber files, the non plated holes and slots are drawn on the outline layer (GML). In addition, there are no pads around the holes. I don't know which of those two criteria is used for the decision to make non-plated holes, however.
