Uzplayer probably has it right: To New Jersey Transit, more riders equals more problems. Yep, that's the philosophy needed to grow the product.
Still, New Jersey Transit itself is in the lead right now arguing for additional service using an additional mode. Up to this point, NJT and NJ-ARP agree. So regardless of which mode is chosen, NJT (and/or we) would be "taking riders away from one line and putting them on another," at least in theory.
It shouldn't matter if -- and we stress this if -- one thinks beyond that "zero-sum" game. That concern may, might, have been something to ponder when NJT was formed in 1979. It has no place in the New Jersey reality of 2006, and in fact has had no weight for nigh on a decade now.
And even NJT, to its credit, is starting to get it, at least where light rail already is proving its mettle. It recently shortened (truncated) the #181 bus line so that it terminates at 48th Street, Union City -- and light rail. The reason? As even the bus division noted, with no shame: LRT gets to Hoboken much, much faster. In turn (NJ-ARP notes in return), NJT gets its #181 bus fleet "freed up" to provide more seats more often to more people. Win-win for both modes; win for NJT; win for the riding public.