Nick
Nice explanation. Yes, you are very correct, my comment was directed at the YEC that light has changed its speed over time, and was one time much different than today, which is absurd. Light does travel at different speeds through different conditions, and that is well verified.
DMP
Dark matter is interesting, and here is a link.
http://www.astro.queensu.ca/~dursi/dm-tutorial/dm1.html