I'll start by saying I'm not an expert about bikes or physics. However, doesn't the weight of the spokes (or any part of the wheel) factor in differently than the weight of anything that's not subject to centrifugal force? In other words, it's harder to spin 36 spokes than to carry 36 spokes in your backpack. I'm still not sure that this difference is significant when it comes to commuting, but every little bit helps, right?

Additionally, I don't think it's really relevant if they weigh less than your lunch or your clothes. Either way you need, lunch, clothes, AND spokes, but if you can get by with less weight somewhere, why not?

FWIW, I ride a Trek Portland with the stock 24 spoke wheels. I haven't had a problem (yet), but I also only weigh about 135 lbs and carry only a small trunk bag with clothes and lunch. It's been less than a year of commuting, so we'll see how it holds up in the long term.