world exploration
“The Mists” are a part of the world environment. Logically, it should be included.
But I see your point. I would suggest taking your group of friends in with you to acquire those remaining points.
No they are not part of the world environment because if they were part of the world environment I would not have to access them using the interface at the top of the screen. If they were part of the world, I would be able to walk there.
By “part of the world environment”, I meant that “The Mists” exist within the same ‘world’ (universe) that Guild Wars 2 is set in. Therefore, it is logical that a 100% exploration achievement be given to those who have in fact, explored 100% of the ‘world’.
Umm, actually you can walk there, there are Asura gates in Lions Arch leading to each WvW map.
Also I have managed to get completion on all four maps with a level 22 alt without being ganked by another player once (although I did die to a load of dolls where someone had opened the present at the Stonemist Vista). Basically I saw the WvW maps as a quick way to extra skill points at low level.