The system in the OM-2 showed an approximation (though under most most circumstances exactly the same) because it used different cells for the meter readout than for exposure.
The readout in the LX is exact, because it uses the same cell for readout and exposure.
The difference with the Olympus and Pentax compared to other cameras really comes at slower shutter speeds, where the entire film surface is exposed. At higher speeds, the meter cell reads the first curtain, then the shutter slit travels across, so as soon as the second curtain is released the exposure cannot be changed. That is why there is no pattern on the second curtain. Up to that point the curtain can be held back, but there are few times the light would change substantially in the few milliseconds between first curtain release and second curtain release at higher speeds.
At slower speeds it's of course different. My LX will time until sufficient light has been collected to satisfy the meter, well below the EV -6.5 claimed, and while 120 seconds is claimed as the limit, mine will time until daybreak, if necessary.