Glad to help, I utilized the services of Monsieur Google and Treks website, you can count the spokes! See, the folks who market a product aren't engineers or even users of that product. The total package is designed to sell primarily and work secondarily. If it sells it works. This isn't rocket science, it's not a fight, it's not about you or me. There are some elements that are bling and some elements serving a designed purpose for use. The Trek 520 has wheels designed to carry weight reliably over time and distance. Just so happens to be 36 spokes. It could also be 32 spokes but 36 it is. Then there's the 24 spoke 720. Sigh. So maybe 28 spokes is better for the 920. But the point is if you're marketing four pannier capability with a big front rack and and rear rack included with the bike you're implying a fully loaded bike capability like the 520. So why 28 spokes and not 32-36?

I am confident 28 spokes is sufficient for unloaded riding with big tires. I am confident 28 spokes with a loaded bike guarantees a rear wheel replacement in a couple years. It's like deciding to putting performance tires on your automobile and being ok with them lasting 15k miles. Nothing wrong with that, look at all the performance you got.