Programmers have the potential to generate a lot of cash in a short period of time, whether through consulting, full-time employment, or through the development of their own software. While you can invest your time in learning new skills, you can also invest your money in assets that are more stable than various programming skills. You can buy property, businesses, stocks, and funds that can support you later on should you tire of learning the most marketable skills of the day. Perhaps this is where many of the web developers will go -- somewhere else less stressful.

I do believe however, that attaining true expertise in one programming field is largely transferable to another field, so perhaps time spent learning programming skills holds it's value relatively well.