The way its used here in aikiweb seems to be an oversimplification of the kind that Chris is hinting as in "good" vs "bad" or mysterious vs scientific.
This link has a pretty good description of the kind of bagagge these terms have , where they come from, and why it makes the current discussion kind of non productive.
What I got from this article is not what it sounds like people here on Aikiweb talk about when they make internal and external distinctions.
If I were to make a very simplistic description of what I read in the article I would say it's something like this:
Waijia (external)- Develop the body to a high level. Make the body strong, fast, well conditioned, flexible and agile. Your body will become so powerful that little else needs to be known/practiced.
Neijia (internal) Don't worry about the physicality of the body, instead use the mind to perfect the way you use your body. You will not need powerful muscles if you use your body as efficiently as possible.
I would say this is a distinction only worth making in the beginning of training. As the article says, as time goes on you'll need both. This is the same with modern athletics, some people just make themselves stronger, some people just practice technique, but only those who excel in both become top level athletes.
Here on Aikiweb, this is not the kind of thing we are talking about when we reference "internal" as IP. IP is suppose to be a different kind of power all together, at least from my understanding.