I think the electric LIRR M1-7 series physically resemble more like passenger coaches rather than commuter except for the commuter style doors. First of all, most commuter cars have 3 doors, but the M series have 2. Second of all, the LIRR and Metro North services are more like short distance passenger RR companies rather than commuter, because of the length of their lines.
Huh? Whats your point?
A commuter car is a commuter car - it has to do with 3-2 or 2-2 all seats and not having anything fancy inside, not doors.
Have you even ever seen an orginal New Haven Railroad coach or commuter EMU???
Out here in the Chicago area, most suburban equipment (except for South Shore) is pretty distinctive because of its bi-level gallery design with center-entrance doors. The former IC electric lines have MU cars that have a basic gallery design with some minor variations. South Shore’s MU’s are single level with vestibules and doors at the end of the cars. The doors are equipped with stairs and traps to handle both ground-level and floor-level platforms.
LIRR/CDOT/Metro North equipment looks more like oversized rapid transit cars than anything else. Compare an LIRR M-1 with an NYCTA R-46 and you’ll see what I mean.