Their results may say otherwise, but MSN are reputedly removing sites for actively chasing any-old-link. A poster in this SEW thread posts what he claims is an excerpt from an email they sent him:
Your site is acquiring links through posting to or exchanging links with sites unrelated to your site content. Techniques which attempt to acquire unrelated spam links in order to increase ranking are considered spam and your site has been excluded from our index as results. Please contact us once you've removed these links and we will reevaluate.
Barry points out the seeming difference in approach - MSN remove you, Google ignore the links. Allegedly.