Mike,
I can't say if clubs will adopt the same mowing method as ANGC, but you can count me as a supt who would choose walk mowing over triplex mowing whenever possible.
My reasons:
Walk mowing is much better on clean-up passes, especially during stress periods for the turf.
Even with the improved floating heads available on riding mowers, IMO walkers in the hands of a capable operator still handle severe contours better then riders.
Walkers are much easier on the collars/surrounds.
No chance of oil leaks with walkers
Although caring for a fleet of walkers is higher maintenance then riders, it's easier to get a walker "dialed in" at low heights of cuts (<.120) then getting all three units on a triplex matched perfectly.
I know all about the lower PSI argument used to sell triplexes-my experience is walkers are still easier on the green.
Although it's the operator not the machine, it is easier to keep a consistent green’s edge with walkers. It's very possible to maintain green edges and size with triplexes, but it takes diligent management.
Having said all that, very good greens can be maintained with riding greens mowers at much less cost.
Don