timdiggerm said:

Is there also an advantage for people with 2.0 setups (like me) in that there's no downmixing going on? The mix was designed for 2.0, and thus will sound better than 5.1 downmix?

Well, in the sense that the 5.1 upmix often involves some audio shenanigans (it's rare that a soundtrack gets a tasteful conservative upmix). So when downmixed to stereo it still has all the other stuff they did to it, whereas the stereo track doesn't have all of that. A tastefully upmixed 5.1 track should sound about the same downmixed to 2.0--it's just that that sort of thing is pretty rare.

That said, Laserdisc 2.0 tracks aren't perfect either. They can have somewhat compressed dynamics (the so-called near-field mix), dropouts, etc, but the audio guys simply didn't have all the tools at the time to be so tempted to make little changes all over the place so easily, so there's at least the semblance of theatrical fidelity.