Alex DH22.
On 700C you want a minimum of 36 spokes. Sure you will hear stories about wheels that took a trashing at some tiny number of spokes. 36 is really the minimum for light shallow rims like the legendary MA2, so one knows it provides adequate spoke support. If you peel away spokes you "need" to go to rims that have structure. That seems to be Brandt's view.
If you are buying all new parts go for 40 on 700C, though most people won't want to queer the resupply situation. I basically build to tandem numbers, that's my weight, and the upper end load weight, it could be as high as 300 pounds on the bike. The fact is that tandems are just bikes, like most bikes they may not get riden all that hard or long so I don't think tandem numbers are crazy for touring bikes if your weight is 200 or up. If you are 150- 200 with no more than 50 pounds gear, go 36 spokes, and if you are 150 down you could go lighter on the spokes, though I don't actually see the point. All estimates are for 700c go down one measure for 26". I don't try to save weight by reducing the number of spokes, you could get better performance by switching to a light inner tube (not recomending that either). Wheels are the defining part of any bike, and the last part you should compromise.
I'm feeling bad about all this right now, I just bought a Rohloff Speedhub which is 32 spokes. I'm going to a 26" rear wheel and the flange is really high on the Rohloff. I am assured that I can't break it. And that is probably true, though I don't much like it.