I don't think the average rider really cares if they get a seat or a prompt ride.
LOL (sorry). So, go to another rail system. The one's I have been on recently have been Coaster in Socal and the line through Silicon Valley. This is your train experience:
1) The train comes. It's the same looking train as the day before.
2) You get on the train. Maybe you have a favorite location to get on the train, but it's the same train.
On the MBTA your choices are:
1) Rotem or Kawaski cars with decent seats
2) the flat with the two seat plasticy painful seats from hell (MBB I thinK)
3) The flats with the 3/2 seats with the half height seat at the end.
4) The flat sets with the rebuilt seats that look like a Rotem or Kawaski car.
As a rider, 2 or 3 usually stink, unless the seats in 3) have been refurbished.
So, yeah, we care.
And, as a rider you tend to learn where to stand for where to get on the car. So, if the trains are a complete jumble this means that you end up always having to move when the train comes. Which increases the dwell time.
Oh, maybe you want to sit at with a desk to get some work done? Then you look for the doubles.
Oh - did you want power to use your laptop? HAHAHA. Well, it depends on the coach. Most Rotems have power somewhere. Some Kawasaki's have power in the doubles near the chair (but it's not consistent). There are a couple of different builds of the Kawasaki's and they are slightly different. OR maybe you got the ones that were just rebuilt from Allstom? that probably has power.
etc etc etc.