I made the 38->30/45->CalTrain or 47->CalTrain ride every single day for nearly a year. It seemed like once a month or once every other month, MTA fare inspectors would board the 38, 47, or -far more rarely- 30/45 I was riding and check everyone's proof of payment. On the 38 and the 47, it always took about five minutes and was a... fairly irritating delay on top of a really irritating commute.
I'm a huge fan of Caltrain's policy: Monthly pass holders only have to interact with a reader twice at the beginning of the month [0]; once when you board and once when you disembark. For the rest of the month the conductors use their brains to remember the current month, and compare that against the end date on your monthly pass.
[0] And -realistically- you don't even have to do that. I went a couple of months without interacting with the Caltrain readers; the conductors never said a thing.
By this, do you mean "I'm the only one who seems to be paying in cash?". If you do, then the vast majority of folks who aren't fare-jumping are either:
* Using a Clipper Card [0] that has a "cash" balance
* Using a Clipper Card that has a monthly pass on it
* Using a Clipper Card that has a transfer from another bus on it
* Using a paper transfer from a previous actual-cash transaction with the farebox
[0] RFID tag which locally stores a balance, a couple of ticket types, and a shocking amount of your fare history. I presume that the data from the card readers on the buses are synced up with some central DB periodically.