Rolling out Firefox or Chrome or IE8 to the desktops would be expensive, but not a budget-buster. Replacing hundreds or thousands of proprietary server-side applications written over the past fifteen years would cost billions and take years, and in the middle of a budget crunch that ain't gonna happen.
(For example: I've heard of one widely-deployed town planning system that requires the users to download a proprietary ActiveX control in order to view planning applications on the desktop ... in PDF format. If you don't run the control, you can't download the PDFs; simple as that. Yes, this kind of proprietary lock-in is insane. Unfortunately, it was procured in the pre-Web 2.0 era when "nobody ever got fired for buying Microsoft" looked a lot more solid than it does today -- and now it's out there in the wild, and replacing it would cost millions.)