Ummm... no - they're not just 1-3 players... they scale according to the type of scenario...
Here's the exact quote. I think you totally misinterpreted what he said... as I underlined the important bits.
Originally Posted by Blizzard Entertainment
These are short instances for a few players. The amount of players will vary on what type of scenario it is. A Scenario could be for three-players for example, and these are all designed for players that are playing their characters in similar ways as when they are questing.
Again, it SCALES depending on the type. The moment I heard this the very first thing I thought of might actually be a cool 25 player invasion scenario if enough people join up!
Ironically I'm not raining on anybody's parade as I actually LIKE the idea of a World Boss working that way... I'm just thinking along the lines of Blizzard - and I can see them more implementing World Bosses via PVE scenarios more than in the traditional way.
I'm just warning people that it might not be the same old method of "Quick! Get your guild together and lets head to that boss before the other guild nabs them!"
Not to mention, how are World Bosses going to work with 10 man guilds? Hell, if they're able to be done by 10 people - you can potentially pug that boss before any guild has all their ducks lined up and in a group.
EDIT: Although I now read the first part saying "These are short instances for a few players" so you could also possibly be right too that they won't extend to raids... (though I can't see why not...). Though 10 people isn't a lot... at least in my book. :P