Yes, different strokes for different folk I agree but that does not mean that those 32 boats using windvane are not also using a generator or are not using the batteries to charge their systems.
I never suggested they weren't... However, I think it is likely that most who have chosen to go with a windvane, perhaps partially due to the fact they require no 'juice', are more likely to be somewhat more conservative/minimalist in their choices re outfitting their boats in other respects...
I agree with you than on an extended passage someone should have a back up in case you have a malfunction on a autopilot even if many circumnavigate with an autopilot without any problem.
But instead of having mounted an autopilot plus a windvane, (that is very expensive, takes a lot of useful space and it is much less efficient in what regard the ability to drive the boat in all conditions) it is much more logical and better to have a set of spars for the autopilot: an electrical engine, the electronic components and fuses would be far less expensive than a windvane. That is what those that voyage extensively in modern boats do.
We'll simply have to agree to disagree on that one... Certainly, vanes have their limitations, and are far less effective in light air than an autopilot... Perhaps my own boat is unique in all the world, but when conditions become a bit sportier - particularly in a quartering sea - my vane handles them far better than my autopilot does... That is simply a fact, one that I suspect is true for many others of us out there who have neither the resources, nor the desire, to trade in our outmoded older boats for something like a Pogo :-)
Older voyage boats have already installed for many years a windvane and probably their autopilot is also an old less effective one so it makes sense that they keep both systems even if at the cost of a lesser performance in what regards to leave the boat on autopilot or windvane, if compared with a modern system.
Again, that is not the case on my boat... My tillerpilot is the latest generation Raymarine 6002 with the SPX-5 gyro, with the "GP" pushrod/motor, sized for boats up to 16,500 lbs displacement... Still, in anything above about F5, my vane simply steers my boat better...
And, as of now, I'm not inclined to invest over $8K for a NKE unit with an internal fuse that can only be replaced by the factory... :-)