Models targeted at DJs will have variable speed adjustment on the front panel to allow beat-matching. Some turntables for home listening will have 2 or 3 speeds with a fine adjustment for calibration.

Rates will be off due to manufacturing tolerance or mechanical wear (i.e. a loose belt slipping on a motor).

Most people don't worry about it.

It doesn't really vary album-to-album, unless you have some ridiculously heavy records that slow the motor.