I've been upgrading my "business casual" wardrobe slowly to include less cotton and more "technical fabric." I wear shirts similar to what the OP showed as undershirts, but I get them at Target or Kohl's. Nothing against Wal-Mart, specifically. I also wear non-specific tech-wear for my commute, but usually change at work.

That said, for weekend road biking, I wear jerseys for all the reasons already mentioned. Alluded to but not expanded upon was the idea of "form fitting." Bike jerseys are not just tight (in fact, they don't have to be tight), but also formed to be comfortable to a rider who is actually riding. (Bent over, arms out front). T-shirts made for any other purpose tend to bunch, bind, and ride up in all the wrong places.

You guys have convinced me on the wool. I'd like to get some of that, but every wool jersey I've seen is over $100. Would like to find some of those big sales, and even in bus-cas, tough to find 100% wool instead of cotton or acrylic. Target had some Merino wool this year that I'm kicking myself for passing up.