We have a lot of upside down calves. Some years up to 10%. This year we've only had 2 so far (out of 130 head calves so far). We watch things fairly closely, and rarely lose one. Backwards calves are not something we see a lot of (or at least if they are backwards, the cows must have them on their own) but usually we'll have 1 or 2 a year. I've occasionally seen the odd one born backwards, unassisted, as well.
We calve in a fairly small lot, but cows are kept out in a larger pasture and sorted about once a week to pull off the heaviest looking cows, so they don't tend to stay cooped up very long, before they calve. Whether it is just luck or genetics or some sort of environmental thing, I couldn't tell you. But we did have a dam and daughter both have a backwards calf one year. Never had issues from either one before or after that tho.....
One thing I have learned from our upside down calves is that, they are carried upside down until just shortly before birth when they rotate to the normal birthing position. So something is stopping this from happening. I personally don't think it is hugely related to BW as we've seen big and little ones upside down.
I would agree, with that quote, some of the time, but if you leave them alone too long, it can be the worst thing for the calf. Upside down, backwards (well breech anyways) and any other malpresentation that prevents the calf from entering the birth canal will delay labour, some times to the point where she won't go into it at all. And by the time you figure it out the calf is dead...