[Sardtok]

Here's a quick and nasty illustration of what normals are, if you happen to remember much from geometry back in high school, this should ring a bell now.
It shows your surfaces on the left, and his surface on the right (as far as I can tell from the picture you uploaded).
So his extrusion would go straight out, while yours would point upwards (you can try manually changing the angle parameter by typing to see if you might have some luck with that).
Now, I expect you know what an average is, and now that I've shown what I mean by normal (although I kind of expect you simply didn't know what kind of normal I was talking about), being a vector pointing 90 degrees off of a surface.
You can probably tell that that vector would point somewhat upwards on the surfaces you are extruding.

Anyway, I need to sleep, and I'm not going to make a nicer illustration of this tomorrow. ;)