I think Castle Stuart is a poor comparison because nearly all of its contours are manufactured.
Tom - I didn't word my sentence properly... I meant to say that of all the "true" links courses I have played (of which Birkdale is one) the fairways there seem a bit less crumpled than "normal," not unlike Castle Stuart's which are indeed completely manufactured. It made me wonder if Birkdale had been intentionally smoothed out at some stage.
I get your theory about the floor between high dunes being less "crumpled," and Balmedie is a good example... but, were those fairways not artifically smoothed during construction to make the course "fairer" (in an American sort of way) to attract a professional event? I thought I read that somewhere.
I don't remember other non-manufactured courses I have seen with deep dune valleys having less crumpled fairways. For example, in Ireland I didn't think Ballybunion, Carne or Portstuart had less crumpled fairways between their massive dunes. Maybe it's an Irish thing!
In any case, I wasn't trying to beat up Birkdale as I really like the course and consider it one of my very favorite to play. I was just curious if there has been a concerted effort to "iron out" the randomness one usually finds on a natural links.