Well, that's why it's not the case that every application and website should worry about it. Which is why the OP's project is so nice: it abstracts the problem

Well, that's why it's not the case that every application and website should worry about it. Which is why the OP's project is so nice: it abstracts the problem into an emulator, so one person can worry about it and solve it for (to a first approximation) all sites on the one side and all legacy browsers on the other side.