I think there are a bunch of different angles regarding this topic, some of which have been discussed before.
One aspect is the idea of branding, and expectations that come along with a particular product by a particular author. Are golfers and clients expecting a particular brand of golf when they note a particular designer? Are people expecting a particular course and experience when they see Tom Doak's (or Nicklaus, Fazio, etc.) name attached to it? Are designers succombing to those marketplace expectations with what they produce?
I certainly don't know for sure, but my guess is that Mr. Doak doesn't necessarily feel he is giving in to expectations, but that he is creating a product that in his mind is the best golf course each site has to offer - within those constraints remains the aspect of what Doak feels is the right thing to do with each site (i.e. his style). Just like the MacD/Raynor/Banks style incorporated template holes, it appear the Doak style is one where the product should appear natural, whether by virtue of the site or by the architect's hand (hope I'm not putting too many words in Tom's mouth) and with that style comes the inevitable similarities whether it be in bones of the course or merely the aesthetics.
I do not have a depth of experience with Tom's courses, but my guess is that the similar aesthetics (which seems to be what is being discussed here) of his courses mask the fact that the holes all probably posess great variety and are rarely repetitive (this probably applies to many architects) i.e. just because many Doak courses have rugged bunkers and a natural looking style doesn't mean that you are going to step on Stone Eagle and say "hey, didn't I see this same hole down at Barnbougle?"
Keith.