Sure, you're going to see instances of higher and lower costs vs. the average...there were a couple of 32GB's that were selling on eBay with about a day left that were close to the $500 mark, but there were also several in that range that were not selling. The average was in the $450 range, those were selling every single time. Looking and high and low costs on year old iPhone's is a bit misleading, and can make you think that the value is higher than it actually is...for example, on my local CL, there's a few 16GB models that are asking $500 for them...for a 16GB. They'll never get it, even new in the package, but they're still asking it, and it would make someone who quickly glances at CL that THAT is the pricing people are asking (because the two were near the top).
You know why you see more of those high or low prices on the sites? Because they don't sell or there is something wrong with the device. The average priced iPhone's sell and the listings are taken down.