I don't think 1 or 2 psi would kill any of us in the scheme of things. A mechanic friend says that 90% of the bikes that come into his shop have extremely low tire pressure, in the 18 - 20 range, basically because most people never check it. And most people don't crash (on every ride, at least
). But if it is important for someone to make sure that they always have the exact pressure they expect, you pretty much have to do it every ride.
For the cupping thing, I've found that different tire models are more or less susceptible to it. Also, riding style (and especially braking style) makes a large difference. If a rider is always on the front brakes while still turning in, that can exacerbate cupping in a front tire. Rolling through the corners on steady throttle seems to be easier on the tires all around. Too low pressure (and perhaps even too high pressure) may cause some cupping over a long period of time, but I don't think 1 or 2 psi off in either direction would be a significant cause for it.
