I think the comparison with the Chivas and Beckham jerseys or Lions sweatshirts breaks down because those shirts are more generally "wearable" than are bike jerseys. (I wear Newcastle and Cubs stuff, myself.) Most major-sport team jerseys can be worn anywhere casual, like to the grocery store or wherever, but bike jerseys are really only wearable while biking.

And I think this makes a difference. If you see someone wearing a Chivas jersey at the local grocery store, you will think that the person is merely expressing support for a team. But if you see someone at the local soccer field showing up with the Chivas jersey, Chivas shorts, and Chivas socks, you are more likely to think, "This guy is really full of himself, he fancies himself a professional." And if he sucks, you are more likely to think of him as a poseur.

If they sold bike jerseys in regular t-shirt form, I might be inclined to get a USPS or Discovery jersey, to demonstrate support for the team. But as a triple-cranking newbie who huffs and puffs up the hills, there is no way I would show up on a group ride in full uniformed regalia.