It’s always been cheaper for anime in general outside of Japan, and certainly for h material. This is not really related to how old the material is; it has more to do with the fact that the rest of the world simply will not pay what Japan will pay. Nobody is going to pay $90 for an h-game when every other game costs $50. ($60 now, and people bitched about that when the price went up for this generation.) Likewise, I dunno what they charge in Japan for h-ovas, but nobody’s gonna pay more than $30 or so in the States.
Since $30 is the going rate for h-ovas, and $50-60 for mainstream games, people just aren’t going to pay the higher price.
Mangagamer (which is mainly run from Japan, I take it) found that out the hard way; they were charging prices close to the original Japanese price, only they hadn’t done any market research. When cheap h-ovas can be had for < $20, I don’t know who they thought was going to buy Succubus Soon! at THAT price.