Hmmm. It's interesting what happens when a few "power users" start using a social networking website such as LinkedIn in ways the owners didn't intend. Two interesting blog posts here: For a New Etiquette of LinkedIn and What Is LinkedIn Doing?
Looks like we're talking about a vocal minority of folks, each of whom have thousands of links. Their point is that they find LinkedIn incredibly useful. LinkedIn's point is that for the site to be useful, in the way in which it was intended, users should know people to whom they link "well" -- LinkedIn believes it's not possible to know thousands of people well enough for them to participate on the site in the way envisaged.
Truth be told, the behavior of some of these self-styled "power networkers" verges on spamming in my personal experience. Nevertheless, I'm sympathetic to both points of view. Ultimately though, it's LinkedIn's ball and the site owners can take it home any time they choose.