Why does every theme have links to all categories in top nav on each post?

I believe it’s remnant from the many magazine themes that float around, and they in turn has taken it from news site who has all their categories in navigation at the top (CNN etc).

The posts themselves usually link the categories for just that post.

Well for starters, your idea: ” It seems like a better idea in my mind to only link to relevent categories for that post, or only link back to home (which then has all the links to all the categories)?” leads to an extra click/step in navigation.
Said that: when accessed from a Category link, WP displays (depending on the setup) contents or excerpts from posts within that category. When I open a full post that way, read it and click previous post then (not standard but thanks to Scribu’s excellent plugin Smarternavigation) on my site you get the previous post within that category. Nice because apparently that Category has your interest.

After reading two or three you come to a really old one that you saw before. Ok, nice, in the topmenu you can switch to another category with one click.
I like it this way. Maybe tags in a tag cloud can get you more refinement, I don’t us ethem.

Thanks for the replies, great ideas

From an SEO perspective, I don’t see it being beneficial to have links in high visibility going to categories that aren’t associated with that post, but I’m not sure really.

@henkholland Firstly, to respond to the extra click in navigation, I don’t see that being too disruptive, it doesn’t make sense to link to everything on your site from each post just so that it doesn’t take 2 clicks to get there in my mind, just my opinion. Also, the way you describe navigating a site, I’m not sure how typical that is?

@wizardregis, i think you’re right, must be just for consistency I guess, seems like one of those things that’s always been done a certain way