For plastic yes, you're right. I tend to use cash for transit fares, I don't know why. I must have some mental block about it, because I'll even leave the station to go use the ATM, then come back and make change and then put the $5 bill in and grumble about having a pocket full of quarters. Oh well, I fail.
One time I got stuck inside a BART station because the machines on the outside take plastic, but the ones on the inside are cash-only. I was 40¢ short and had no cash. The person at the station let me through though.
Another one of their design decisions that makes no sense :)
