[tytso]

If you are going into the city anyway for work, you can drop off your passenger near a subway stop, and continue into work. The assumption is that you were driving anyway, and so the cost of adding a carpooler and dropping him or her maybe 3-5 minutes out of your normal drive.

You're right that if you need to go out of your way at pickup or dropoff, or if you weren't going to drive into the city anyway because parking is $$$, this isn't going to work for you. But then that wasn't the intended target audience. If the goal is to get cars off the road, and you weren't going to drive, but take light rail as the saner way to commute into the city --- then by all means, continue using rail or light rail for your commute!