As I suspected above the PDF version of Google's O'Reilly offer is just a (bad) conversion of the epub version
https://twitter.com/martinkl/status/880541924335267841
I suspect if Google does not care about the PDF version the epub version is made unenthusiastic as well.
O'Reilly's explanation is a little bit flawed because they could keep it's e-book store open without too much extra costs. The format (epub, PDF, mobi) probably still need be there anyway for the other shops and the creation of the paperback version.
After a few days I am still very unhappy and disappointed so my money will go to other publishers in the future.