Ithink at DAZ there is pressure for the vendors to only support Studio. Honestly, I don't see where vendors who only do props, especially the simple static ones, or poses should have that much of a problem making products for both Poser and DS. I can understand it from the perspective of someone who's never used Poser before. I have the same problem understanding DS. But someone like Faveral who's had experience with both...
The relevant bit being the words 'I think'. Daz really don't care as long as stuff is selling. It's not just the 4 different render engines that the vendors have to cater for, things like instancing isn't supported by Poser nor is LAMH, just a couple of examples that has made it difficult to produce for two different software that have become less compatible as time has moved on.
Vendors who were once comfortable with Poser may not have purchased the more recent releases and so are stuck with older versions and cannot therefore produce for the latest addition.
As to increasing the pricing in line with the extra hours it's taken - personally I am not going to pay a higher price for something I don't want - so split the product into DS and Poser versions, which I believe was tried by some vendors and they just didn't see the sales to make it worthwhile.
Poser users were and still are very vocal about what the think of Daz and that they will not buy there, I've even seen the criticism and insults aimed at the vendors themselves and their products; why do think they would feel inclined to work extra when they come under the sort of criticism that often permeates some forums.