With your refined-scope question and statement you're "basically the only FS developers"
Not "the only FS developers", but the only ones that will have to put to much effort in what WE considered to be an upgrade worthy enough of an update price, due to how we do things.
Maybe we are wrong, maybe it would be better just not to care about performances and future-proof so much, and simply tell users "just use the DX10 fixer". Maybe it would be easier if we kept doing things the easy way, so we won't have to work so hard when updating, so we could offer it for free, since most user won't really know the difference anyway, and would just upgrade (spending way more), by upgrading their hardware, not really getting so much bang for their buck because, incidentally, the scenery that benefits more from an hardware upgrade (GPU, most likely) is precisely the one that doesn't contain legacy code.
I never trying to say we are any better than anyone else just that, when we offered what we considered mid/minor upgrades, still containing old code and not revamping the foundations from scratch, we DID offered them for free, for Zurich (twice) and KORD. The free Zurich update HAD a new Terminal. The issue is, a new terminal is something that everybody understands, and it "looks" like a major upgrade, but it's not nearly as long or complex as workload like redoing the ground entirely, which is why nobody else is doing it, surely not as a free patch.
