I tore up my lower back in high school. If I ride a bike with a completely upright position it results in quite a bit of pain in my lower back.
The bizarre thing is that my saddle to bar drop is fairly large on my fixed gear road bike and my CF tarmac. I find them quite comfortable. I do stretch daily to keep my back somewhat limber.

Even my MTB has the bars a tad lower than the seat.

As for the comment about riding a unicyle in college, I am assuming that poster was at most in his early 20s. I did quite a few things to my body back in my early 20s that it can no longer stand now that I am in my 30s. I am assuming this will continue to change as I age.