Oh, I must have forgotten to mention, of course we don't use our Taq
polymerase for PCR. We use it in storage buffers as a stabilizer, much
like BSA :)
As pointed out, anyone can purify any enzyme they damn well please, as
long as patented recombinant organisms are not involved.
The idea of cycling the temperature of an enzymatic reaction was proposed
long ago in standard scientific publication, and the application of
the various thermostable polymerases to this procedure may well have
occured in the absence of any patented process per se.
I can assure you that the proper legal aspects have been considered.