A kettle might cause a branch circuit to trip - but the whole house??? If that happens you have bigger problems than a kettle.
(Plus in the UK plugs have built in fuses should trip first. So it's pretty doubtful it was the kettle.)
http://www.ctm.co.uk/gallery/Electric/Electric_photo_gallery...
RCDs detect the slightest earth leak, so they are far more likely to trip than the MCB or the fuse on the plug, which only detect a sustained over-current.
No it wouldn't.
You could stick the bare wires of a branch circuit in water and it wouldn't trip the main breaker.
The main breaker will trip if there is a short inside the panel (which is all but impossible unless you are working on it live - which is sometimes done). Or if you used so much electricity you simply overloaded it, but if you did that you have the wrong panel for your house (or you are running some crazy equipment - arc furnace, maybe).
Generally the wiring goes: mains input -> 1 or more RCDs -> several circuit breakers -> several outlets -> fuse in plug -> appliance.
So a grounding fault can take out many circuits, and many-lots of sockets.
That must cause so many nuisance trips - doesn't seem like a good idea (kinda like the ring circuit that to this day causes trouble).
In the US you can have an RCD (called a GFCI here) in the panel, but it feeds a single branch.
RCDs are expensive, so the most common solution is to have two RCDs, each protecting half of the circuits.
It has a split in the bus, so there are two RCDs, one on the left with a couple of breakers and one on the right with the rest of the breakers, and a separator in the middle.
Like:
supply in -> R-B-B | B-B-B-B-B-R <- supply in
C R R | R-R R R R C
neutral -> D-K-K | K-K-K-K-K-D <- neutral
Also, @alextingle, I didn't know that you were meant to have two separate circuits, although that makes sense. Lots of things are required to be RCD protected in the UK, so as you say, it makes sense just to put everything behind an RCD. We don't get any nuisance trips, which I attribute to a generally higher standard of wiring, earthing etc. in the UK, although that could just be jingoism :) (I did once live in the US and some of the literally fraying wiring connected to two pin sockets with no earthing in the house I lived in scared me.)
Newer installations will often have an the RCD integrated with the regular circuit breakers, so you get one for each branch (as well as one the covers the entire installation).
Of course, if you buy something from the store and it trips your RCD you know it's got a fault so you return it. And if something old starts tripping your RCD you know it's developed a fault, and you fix it or replace it.
It seems crazy to me, but if they do that, then they do that.
Wrong is relative: here in Portugal we pay a fixed monthly fee that is proportional to the maximum load. Having the "right" panel may cost you more even if you use less electricity, so many people choose to carefully manage their loads instead.