My guess is that a boss in a Cata heroic will give 10 JPs and raid bosses will give... more than that... and WotLK bosses will give 1 JP. That way there's an incentive to do the new content, but old content is still worth *something* also.

It makes sense, at least - they don't want you saving up all your points to instantly get fully geared when you hit 85, especially since you only killed level 80 bosses to get the points.