seeker333

More spokes are better for wheel longevity, and the incremental weight added by a few spokes for Touring use is utterly trivial. Well built 36h, 135/100mm QR hub wheels are fairly common among the Touring crowd because they are sensible low-cost, low-maintenance, proven wheels.

The Surly LHT, probably the most popular touring bike ever, uses mid-tier Shimano ball bearing hubs, inexpensive Alex rims and 36 straight gauge spokes. I cannot recall a single thread on the Touring forum where someone complained about the cheap wheels on their LHT. It is unnecessary to reinvent this wheel for touring.

The fact that the Trek 920 has 28 spoke wheels is not it's major shortcoming; rather it is the fact that the 920 frame/fork will accept ONLY 142-12mm rear and 100-15mm front thru-axle wheels. These will likely be a special order item at any North American LBS you'd stop at for a wheel replacement. If you plan on touring outside NA the Trek 920 is not the best choice.

I'll conclude by noting that steel is well known to be a more durable material with a fatigue limit that is several orders of magnitude greater than aluminum. A well built steel frame can last lifetimes if protected from corrosion. An aluminum frame can fail in relatively short time used regularly in a rough off-road setting, which makes the choice of Al for the Trek 920 all the more puzzling. Evidently Trek is aiming for the MTBing crowd with this bike, and since more than half the bikes sold spend their entire lives in a shed, basement or garage, Trek probably isn't risking much in the design of the 920.