If you hold the dead fob against the little key symbol on the steering column it'll power the fob by induction and you'll be able to start the car.
You're right, older fobs that just do keyless entry may not be able to start the car though.
The poster a couple levels up said people where paying full towing price to have cars moved 5m. If you can put the car in neutral you should be able to push it that far yourself.
The main problem would be having a locked driving wheel (common in France), which may make pushing it 5 meters away impractical/impossible without lifting the front wheels.
And there is something to be said for not being that guy who says "should have read the manual!" when another human being, however flawed, gets stuck in a situation they don't know their way out of.
It seems like it would be worthwhile for the industry to come up with a standard symbol for “hold your key fob here to make it work when the battery is dead” and print it on the appropriate spot on the car.
So there are definitely circumstances where the phi’s always artifact alone just isn’t enough to start the car, only to get in.