Are they higher then the cost for the Windows binaries? I doubt it.
So who cares what it is what I pay for? Money is money, no matter what it's intended for. If I give you 10$ for foo, and then take back those 10$ in order to give you 10$ for bar, you're left with 10$ anyway. :P
It costs X dollars to make a Windows version. It typically costs 10-15% more to make the thing properly cross platform- and if the studio doesn't design it the right way (which is disturbingly often...) it can cost much more than that. Depending on how clean the version is, a porting interest can expend 5-10K in labor, possibly more (more like probably so...), just to migrate the codebase. If it was written with a bit of portability in mind, it's only the 10% that the porting studio has to incur. That's if they're lucky. If not, it can cost as much as 50% of the development cost making the title happen.
This doesn't even get into the part where the studio/publisher doing the porting work has to pay royalties up-front to even have the privilege of porting the thing in the first place. There's another $10-250k right there. And that doesn't get into the cut of the proceeds that's due up-front before you get 'em to make a production run for the title.
Your $10, multiplied by 2000 units (which is what most runs for Linux currently comprise...more would be insane...) would amount to $20k which comprises the typical porting royalty for a good title and doesn't cover the per-unit royalty.
It's not fungible. It's not the studio doing the porting work (You'll note that the binaries you were able to get were all done by the studio that made those games. They expended the 10% or so extra themselves because the effort paid for itself in more robust code.) then someone will have to buy the rights to do the work and that cost has to come from somewhere (which is why you have to re-purchase the Linux versions...).
Many publishing interests don't see support and lost good will costs as being something they need to offset and don't care about the portability- it's extra money and extra delay costing them time to market to them. And, unless you're talking 20k units (something the Linux community has YET to have for sales on ANY game to date- mainly because of the attitudes you espouse, unfortunately) these studios won't even think of you being "more money"- seriously so.