@ Peter Payne
"Steam patches are part of the overall business environment of selling 18+ software in 2015."
"Among other things, we can't charge a price that the Japanese parent company will agree to let us charge."
If "official" steam patches are part of your business strategy going forward and the JAST store prices are fixed, then I'm in agreement with Dark Shiki that this is something that needs to be looked at.
For one this setup will obviously preclude simultaneous adult and steam releases as is MG's current practice. I don't think it'll hurt steam sales to release their version a few months after the adult version but I am concerned about current JAST customers who may decide to wait for the steam game.
The JAST download does offer some benefits (earlier release, no patching required, and DRM-free) but I'm concerned these benefits may not be strong enough to stop a significant segment of your existing customers from delaying their purchase until the steam version is released.
If you're going to keep this model in place you'll have to add some value to the JAST downloads. Obvious choices would be digital soundtracks and art books, however I don't think that would be strong enough of a deterrent. Maybe the ability to later purchase ome heavily discounted hard copy on j-list could be another benefit (not sure how the JAST and J-List are different companies thing would come into play though).
Another idea would be access to an exclusive mobile version download (adult and/or all ages) of the game that comes with your adult version (dl & hardcopy). I'm not sure if there's enough collective demand for such a version or if the development costs would outweigh the loss in revenue from cheaper steam games but its something to consider.
I do understand your current strategy though. All your games are DRM-free so a steam patch is only a matter of time (might as well give your new steam customers a helping hand) but at the same time the loss of revenue is something you should look into especially if you're considering to increase the volume of games sold on steam.
As a reference point, I personally hold out on all of MG's initial game releases until they either release a hard copy or I'm certain a hard copy won't appear and they put the game on sale for 50% off (the only exceptions I've made to this rule thus far is for the three Lilith games they've released).
Another approach to steam all together would be to raise the steam price much closer to your own digital price and to effectively use the steam page as an advertizement for your adult versions that include a free steam key. Most of your steam revenues would come from periodic steam sales. This method also wouldn't preclude a simultaneous release for the adult and steam versions. I think this is the approach a Japanese company would use but it may result in you loosing more money than you would under the current approach (with the tradeoff being higher visibility for your own retail sites).
Sorry for the long wall-o-text post; just wanted to share my thoughts on this issue.