I think what he means is, that on a clean install at a OEM Computer, the Setup uses the Product Key of the Core Edition from the BIOS, so that you cant just install the Pro Edition. But what i still do not know, if it maybe works if you user the "pid.txt" file in the sources folder, or use a "ei.cfg" file.
Im pretty sure I read a thread this morning on using the pid.txt otherwise it would report an incorrect version install