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3-4 weeks ago I was reading on the blogosphere (sorry can't remember which blog) where a scout was giving some insight as to what they look for, and he indicated that a team will give a player more opportunities if he shows either power or speed. This is probably why you will see a higher number of 'older' power hitters breaking into the league at a later age, and also on the speed side an occasional Scott Podsednik.
For pitching it would be analagous to power pitchers or crafty left handers.