The end portal is something in minecraft that is rare. The only thing that you get XP from (not going INTO the portal) is from the Silverfish spawner, which isn't very much. We kinda deserve the more XP, just because we found something as rare as only 3x a world.
This isn't for when you GO into it (as I stated), rather just for FINDING it.
Also, here is an awesome suggestion I had: http://www.minecraftforum.net/topic/1745550-biome-effects/
It wouldn't have to be big, at least a few levels, but all we get is 4 xp bubbles for finding it (silverfish)