and famously if there's ever a blackout, most of modern ovens will refuse to work until you setup the clock... never seizes to piss me off each time I have to do it...
This is a security feature. Most modern ovens allow you to set a timer with auto shut-off. This is very useful if you want to go out and come back to a ready meal. You can imagine what would happen if the power went out for a while and after it came back the oven switched on automatically. Refusing to turn on the oven when the clock is not set is the easiest way to prevent problems when it is in use.
good point... still, quite annoying when you come to check your meal cooking in the oven for the last hour, only to find out that it never actually switched on because of the clock :)