Mike
The whole system works on the basis that each State provides briefing services only for flights originating within its own airspace.
I thought we did this one to death in various places already.
Assuming that you have a plane with sufficient range then any route could be flown with a
UK departure.
So
UK AIS must deliver
enroute notams for any route, anywhere.
You could then land at any airport capable of receiving international traffic.
So
UK IAS must deliver
airport notams for all airports capable of receiving international traffic.
I know what you are getting at (e.g. briefing a flight from Germany to Spain using an AIS website in Mongolia) are officially frowned upon because everybody would congregate on the one website that is most usable; such is the internet...) but the reality is that the information cannot be restricted in that way.
The only restriction I know of, and the only one which I have ever seen you or anybody else list definitively, is the French domestic (D series) notams which they deliberately do not distribute to non-Schengen states, presumably on the basis that nobody outside Schengen could fly there anyway. But then if you fly to little fields within France, you also have to speak French...
As for the certification of AIS providers, I could get very cynical about this.
The UK Met Office has a good weather model for the UK but it is not made available to GA - except for TAFs/METARs (which you can get from anywhere anyway), MSLP charts (likewise), the famous F215 and similar very basic stuff, of minimal use for IFR. They don't release the really good stuff like the 3D model which would enable vertical profile forecasts to be generated. This kind of stuff is sold to commercial weather briefing packagers, who are obviously not going to stick it on a free website.
The only bits of the UKMO data that "leak out" in various corners of the internet are ones which the UKMO has to supply to other countries, and some of them choose to publish it. Like
http://weather.uwyo.edu/upperair/sounding.html which (University of Wyoming) is where you find ascent (skew-t) data for the UK and Europe
So a lot of people, and most of the "unofficial" weather websites, use the American-run worldwide GFS data.
I reckon this certification is something which the weather data industry has lobbied for, to protect the resale of their data in the face of more and more stuff slowly finding its way onto the internet.
I also reckon that this certification is going to be meaningless, in the context of any amateur website, and also in the context of any website hosted outside the EU. They might just have to get their data feed from somewhere outside the EU.
Crude protectionism, that's all it is.
For me, I just love to find the occassional nugget like
http://www.meteox.com weather radar (warning: N Italy feed seems to have been pulled, which is why N Italy looks very clean) and
http://pages.unibas.ch/geo/mcr/3d/meteo/ which AIUI was just somebody's PhD project but which is the sort of stuff which the UKMO should provide to all pilots.