I would say they do work at least some of the time!!

The best for this was Mighty Mouse. I could go off praising this little robot as it was one of my all time favourites, but I will resist the temptation.
The trick I think was to keep the robot narrow and the centre of gravity very low, also I think the roll-over bar was oval, and in the last few years held on by springs.
I would love to make something like MM myself.