Why the difference?

I'm relatively new to vinyl and as such I'm trying to understand and learn the medium a much as reasonably possible. To that end can some one tell me why the way a turntable is driven changes/effects the sound. For instance, I read things such as how idler drive system give more "drive" in the music. Nebulous statements like that don't do guys like me much good when trying to compare belt driven tables to direct drive systems. Maybe I just can't read between the lines of text that well. I'm sure if any drive system is built well they will sound good. However, it seems over and over again there are certain attributes attributed to certain turntable drive systems. Why is this? Why would an idler drive system have more musical "drive" than a belt driven system. What's it doing that is so different? I would imagine 33 1/3 rpm is 33 1/3 rpm - though I do recognize no rpm is perfect and there are small variances. And what the heck would more "drive" sound like? The only thing I can think is that the drag of the needle on the vinyl causes the platter to vary from a constant speed depending on the frequency in the grooves, and maybe some drive systems reduce the tendency to vary from 33 1/3 rpm more that others. Though this is pure speculation - and still it doesn't tell me what the heck "drive" is suppose to sound like - or maybe it's feel like.