I fully agree that composition and a natural raw talent are key.
However, when one does capture a truly 'great' shot...using pro grade glass/equip...will just make that 'great shot' IQ an extra step higher.
It's the same with music. Joe Satriani will sound great playing guitar through even a modest/budget amplifier system. However when he uses his $250,000 stage rig..it just sounds that 'extra' bit amazing.
There's a reason that professionals use pro level gear or tools.. Even my high-tech running clothing/shoes/etc makes a difference when I'm out on the road during a 10K, half marathon, or whatever. It provides an extra 'edge' that lower performace just gear doesn't. That difference is always a combination of several factors, each providing a small step up, that together kicks it up a notch or two.
Photography is no different in this regard. Here's my short blog on the subject:
http://geofflawrence.com/blog/?p=377
Also,
Diffraction beyond f/16 is not really such an issue anymore (especially with todays editing software) and modern tilt/shift lenses...f/22 and even higher is regularly used in commercial product photography.
KEV