Video on DSLRs kinda happened on accident, where an engineer thought of taking video technology they incorporated in point-and-shoot cameras and putting them in a dSLR (5dII) in case people wanted to take casual video clips. Then Vincent Laforet took a gamble and proved these video modes, while just an afterthought, were actually incredible. So as far as the 5dII is concerned, I'm guessing the development cost for the video mode would probably translate to a 5$ increase on a camera that sold for way over 2000$.
Then Nikon got jaleous and started working on their own video modes, mostly just to compete with Canon, but again focusing mostly on what they were good at: insane ISO, but mostly offered 720p options.
Then Sony came in and incorporated technology it had learned from their P&S but also from their camcorders and brought in autofocus.
So basically whenever those big guys bring out video features on their DSLRs, the R&D has mostly been absorbed by either their P&S or their camcorder counterparts.
The only extras you can think of lately is the extra plug they added for audio monitoring (such as headset), which I'm sure costs less than 1$ to manufacture.
That's also why you don't hear of companies such as Hasselblad offering video modes, for them it would probably be a billion dollar investment.
For Canon/Sony/Panasonic, and somewhat for Nikon, it's just a matter of asking an engineer working on the video side to send them some code, then adapt it to the DSLR.
On the other hand, if you're never gonna use video, you might want to skip technology like STM, which I don't think will improve anything on the video side, but I'm looking forward to seeing the test results of the AF system on those lenses, as well as the image quality. In any case, the manufacturers need to add an AF motor anyways, and it's probably not that much more expensive to put an STM instead of USM AF system.
Cameras: Canon EOS 6D, Canon EOS Rebel T3i, Canon EOS Rebel T2i, Canon S90
Lenses: Tamron: SP 24-70mm F/2.8 Di VC USD, SP 70-300mm F/4-5.6 Di VC USD, Rokinon: 8mm Fisheye cine, Canon: EF-S 18-55mm f/3.5-5.6 IS Lens, 75-300mm f/4.0-5.6 III, and EF 50mm f/1.8 II
Retired camera: Fujifilm Finepix s700