If the mirrors folded automatically when the ignition was switched off, then presumably they would unfold when the ignition was switched back on. Perhaps not such a great idea if, like me, you park in a garage with a narrow doorway. I want those mirrors out of the way when I'm reversing out 
That is
exactly the point!
I had a Focus as a hire car once (only had 4 miles on the clock when I picked it up, and I got nicked for speeding approximately 20 minutes later, you can't win). Anyway, I was visiting my mother at the time, and made sure to put the car in the garage because I didn't want any of the locals getting any ideas. Its automatically-folding mirrors were a pain in the neck.
First, I had to fold them manually in order to get into the garage in the first place. Then, when I started the car, still in the garage, the damn mirrors promptly unfolded. The last thing I wanted. So the first thing I had to do before I moved off was fold them again. Then once I was out, unfold them.
I was really keen to find out if there was a way to disable the automatic mirror folding, but I only had the car for a few days. I'd forgotten all about that till I started reversing the new GTi into my garage, and remembered the hassle. (What I hadn't figured was that for reversing in, I need the mirrors to get the car properly lined up. So I have to wait till I'm almost at the doorway before switching them to fold!) Then of course they're folded for me to drive out, and once I'm in the driveway, I just turn the switch again. Perfect.
Automatic folding is a really silly idea, not until they develop something that will automatically sense a garage door coming up.
(Reminds me of a brain-dead feature on my XR2. If you opened the driver's door with the headlights on, it squawked annoyingly at you. All the time you were opening the gate or whatever. There was no way to stop it, short of disabling the feature entirely. I complained and I moaned that, very useful though it was, I only wanted it to do that
when the engine was switched off! I did
not want it to do it every time I nipped out of the car for a minute after dark - for example to open a gate. But nobody could fix it. The designers must gave been really stupid. One of the reasons I got rid of the car after only 5 years and bought the Peugeot, which was a bit more rational.)
Rolfe.
ETA: Imagine parking very very close to a wall, having manually folded the mirrors to do that. Then you get back in and switch the ignition on - and your nearside mirror unfolds smack into the wall! I can see why they wouldn't have it as an option.
