[thejeff]

The difference is the staler isn't playing.
Generally one subs a staler because you suspect he's gone, not because he's been missing turns. I've never seen someone who's missed turns but still wants to play get subbed out. It's usually either people who don't respond to messages after missing a couple turns or people who miss a few turns then admit they can't keep up.
Of course, I've also never seen a case where someone stays active on the forum, claims to want to keep playing but doesn't actually send in turns.