cyccommute 

Given the design of wheels and spokes I'm not sure that I'd agree even if you don't overload a wheel. For most hubs, the spoke hole is 2.3mm in diameter, a 14 g (2.0mm diameter) spoke doesn't fit in the hole of the hub very well. Since the wheel is a dynamic structure, the rim is alway flexing up and down as it turns. Each time the spoke flexes there is the possibility...and even the probability...that the spoke moves up and down that 0.3mm. On a thin wire like a spoke there is only so far you can force it back and forth until something breaks. Of course putting more stress on the wheel by loading the bike with a large person and a large load isn't going to help.

The failure of spokes because of movement is the reason that I build my wheels with Alpine III spokes. There's no room for the spoke to move...okay, maybe 0.01mm It's worked well enough that I have a 5+ year old mountain bike wheel that's the first one I've ever had that hasn't broken any spokes in that amount of time.

I was puzzling about this topic this morning on my ride in an wondering if straight pull spokes wouldn't be a better choice for touring. No bend to flex or be the weak point.

Hocam

Actually the spoke would only move if it were to lose all tension an go into compression, otherwise the tension keeps the elbow against the hub in the same spot. This would be extremely unlikely because usually each spoke carries something like 60 kilograms of tension or more and you're typically loading 4 spokes at a time, maybe 5 if its a 36 spoke wheel.

Read "The Bicycle Wheel" by Jobst Brandt.

Butted spokes are actually more fatigue resistant than straight gauge spokes.

The "weak point" is actually at the nipple and at the elbow where most of the stress from concentrators like threads and the bend is. By butting the spoke the middle will flex the most while the thicker ends will be effected less. This distributes the stress instead of having it even higher at the ends of the spoke, extending fatigue life.

Butted spokes make for a longer lasting but not quite as stiff wheel. Straight gauge spokes will build a stiffer wheel but it won't really be stronger.

grolby

This is how I feel about load distribution, too. I strongly dislike the sensation of the back wheel trying to push the front to the outside of corners. As the load gets bigger, the feeling that the front wheel just wants to keep plowing along in a straight line instead of tracking around the line I'm trying to set with the handlebars just gets stronger and stronger. This was worse on my old Miyata touring bike, but it definitely happens on my much nicer Surly LHT as well. Recently, I've tried throwing my bags on the front rack. The difference is astounding. Steering is a bit slower, but the effect on handling is almost as if the weight weren't on the bike at all. The next time I tour, I'm downsizing the rear panniers and putting more in front.