Well, the manga in question are out of print, so they're usually near impossible to obtain. But I agree either way.
Not really.
Even if they're out of print, there are literally hundreds of thousands of unsold copies that are sitting in warehouses waiting to be ordered.
For example, I got my Mabinogi Succubus figurine for the exact same price it was initially sold even though its been out of production for well over 4 years when I bought it.
My middle school english teacher had some sort of obsession over this really outdated starwars card game that hasn't been in print for over a decade now. He can still order them for the same price.
This isn't always the case with every item and eventually the supplies to run out, which in turn tends to raise the price a bit.
Example:
N64 games are 50 dollars on release.
Once it is no longer popular it is 30~40 dollars.
Once it is no longer in production people begin to trade/sell it for about 20 dollars.
Once the supplies completely run out people start selling it for 35 dollars.
This actually pisses me off. I want Mario party and Kirby 64 but they're far more expensive now.
A series like Love Hina, you can find almost anywhere even if its not in production anymore.