Ah yes, I remember my own early homerecording days with 4 Track cassette, it was very frustrating trying to get a good stereo mix. I guess a lot of it was lack of experience back in the 60s. I've even heard albums recorded on eight track in the 60s have the kick drum far left and the rest of the kit far right, I suppose it took a while to realise that things like that didn't sound right. I suppose it is easier for us now, trying to copy good mixes, when in those days they where creating them with no reference points.
Then of course you have Lenny Kravitz who's recreating those mixes with the drums panned way over to one channel, to recapture the sound of that era.
Another factor is that some of those mono mixes did have elements that weren't used in the stereo mixes, like the mono version of Piper At The Gates of Dawn. So I guess there's also that element, that it's not necessarily better because its mono, but better because it a better mix. That and people probably heard the mono mix first and that's how they remember the album.
I've just tried remixing one or two of my songs in mono and remembered what Farview said about mixing in mono and then panning. It's a method I've never tried before and it did make me think a bit more about eq. I'll have to have another listen once my ears have settled, but the stereo mixes did sound better than my previous mixes of those songs.