I think connecting the feed to each breaker with a wire link must be another common European trait, as it's done in France as well. It's rare in the U.K. though, except in the case of some small DIN-rail enclosures where there are perhaps just one or two C/Bs.
There's nothing in our rules to prevent the use of a double-pole C/B opening both hot and neutral, but it's not usually done that way (I don't remember ever seeing such an installation). GFIs are a different matter, as they always open both sides of the circuit.
I can see a practical advantage of using D.P. breakers where there is a main GFI. If you turn off a C/B to work on one branch circuit here, although it's safe to touch the neutral is still connected through that GFI. If you accidentally short the neutral to ground (e.g. while cutting a cable) it's possible to trip out the main GFI. (Really annoying if you're working in an attic and your floodlight goes out!) No big deal really, but it means having to open up the panel and disconnect the branch neutral instead of just flicking the C/B off.
By the way, many new installations here do have a main GFI even when not actually required.
