I read Wikipedia a lot and I always enjoy clicking on date/year links, or using popups on them, because I am interested to place the information I read within a historical context, which is rarely provided by the article text.
Often I am interested in historical context not directly related to the article itself, for example if I read about a person born in 19th century Europe I may be interested to learn how 19th Africa was like. The reason is that as a reader I read in a nonlinear way and I like to integrate information in new ways.
Furthermore, I use dates and years (as well as geographical links) to escape from a set of interrelated articles when I lose interest in them. This is also why I like links that are not relevant to the context: if I am reading about pop music and all links are also about pop music and I get bored about pop music then I cannot escape easily, unless there is a link not relevant to the context so that I can jump to another theme of articles. Linked years, geographical terms, and "irrelevant" links provides me with the opportunity to read Wikipedia in a nonlinear way, hopping from theme to theme and returning back as I see fit, and integrating the information I read in my way.
However, delinking dates and years, or only allowing links directly relevant to the context, denies me the opportunity to read Wikipedia's historical information in a nonlinear way easily, as I have to use the search box, which I very rarely do (and with the skin I use, Nostalgia, is not very easy to use because I can't see easily the Ajax suggestions, it's bug 15902 for which I have provided a patch on bugzilla). Without year links and "irrelevant" links, I only have geographical links to escape from a theme of articles (and I don't use the random page feature too often becaue it usually only returns me pop music stuff or American villages), and if an article doesn't have them then I am stuck with reading in the oldfashioned linear way, therefore my reading experience as a reader diminishes and I get less value from Wikipedia compatred to what I could get if the years and "irrelevant" links were left in place.
Hoping this will provide an insight into why some people want years linked and why they so like to build the web.