I think the rub is the fact that the Feds own the document (the paper), while the company has the intellectual rights. Univair told me straight out that they got busted for overstamping a federal document with the aircraft serial number. The only way that would be OK is if the STC was granted for just one airplane rather than a series.
I'm sure the companies like it the "old way", but I think that ship has sailed.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65