I noticed this when looking several years ago, though I don't know if it was a local aberration or standard for condos. They seemed to behave like new cars, in that the first owner loses significant value just for driving it off the lot, so to speak. I saw numerous examples of people selling 3-year-old condos for 40% less than just-completed condos elsewhere in the development. New condos in the southwest suburbs were generally $75k-$150k. Same locations, 3-5 years old would run $55-$120k.
The psychology seems to be that people don't view condos as the same as houses, but as apartments you can claim on your taxes. And new apartments are better. I'm sure in urban areas (New York in particular) condos are seen more like "real" houses.