That's a completely seperate phenomenon
. Regular links that go to wikipedia articles were put there by the blogger, presumably inspired by wikipedia's habit of cross-referencing. It's actually extremely useful within wikipedia, but I agree it can be pretty pointless outside of that. (Although I must admit to linking to wikipedia articles that no one will probably read).
The ad-link things are much more annoying. Usually in my experience they're green links, that have ads pop up when you hover over them, and are trying to sell you crap. Planetgamecube
has them now and eventually you get used to them. It was annoying at first because it's intended to look like it's going to take you to a wiki page, or the site's relevent page (for instance, in the PGC example, I'd see "Mario Tennis"
underlined in a review of something else and go to click it thinking it'll take me to PGC's Mario Tennis page, but it's actually a freaking ad for some game store site trying to get me to buy Mario Tennis.) This also leads to phrases like "no doubt"
being linked to CD's when someone was just using the expression.
blogs generally don't have that sort of ad, to my knowlege.
/note: Either PGC stopped doing that, or my adblock stops me from seeing it now.