Yes you're both kind of right. "Dark matter" and "dark energy" are both "fudges" to explain why observations of the universe do not match what you would expect from basic theory such as Newton's laws. As such in a way they are kind of honest calling them "dark". However they are not just place holders and do relate to fairly defined explanations for the anomalies - well in the case of dark matter especially.

The numbers you give WG are right if WMAP is right and if the main fudge theories are right. There are big questions about both. And what you say about dark energy is pretty much right but dark matter is not like you describe it. Basically its the way galaxies rotate that doesn't match the theories - essentially the edges move faster than they should considering the mass of normal (baryonic) matter within the galaxy. "Dark matter" is the explanation most scientists use to explain this. Basically they think that there is another form of matter which only interacts with normal matter very weakly - which makes it very hard to 'see' other than by its effects. One reason cosmologists like the idea of dark matter is that is helps explain why the universe is "clumpy" - why it has structure rather than a kind of uniform diffusion. But the fact is no dark matter has ever been detected despite attempts, and there are other explanations that could explain the rotation of galaxies without inventing any missing matter. One obvious suggestion is that gravity does not work as we expect over long distances (this is called MOND - modified Newton).

The thing is we don't really know much more about gravity since general relativity - we just have a lot more unproven theories. I expect that if we really understood gravity properly it may well be that the interplay between mass and spacetime has a more dynamic relationship than currently understood. As such large scale phenomena such as galaxies could exhibit effects more expected in fluid dynamics than in basic laws of motion. But thats complete speculation so who knows.