For starters, it is becoming the best hiring tool on the planet. It's already strong, with 6.5 million job listings, and 94% of recruiters use the site. (source). But it is inherently superior to its competitors because recruiters can compare candidates claimed experiences with their professional social network.
LinkedIn will beat Monster in recruiting for the same reason that Facebook beat MySpace. Even though MySpace, at one point, had more registered users than Facebook, the lack of stricter identity control (i.e. a REAL, non-spammy userbase) led Facebook to win in the long run.