Great idea in theory, unworkable in practice for many businesses due to cost. For instance, IIS6 cannot support TLS 1.1 or higher (unless MS decide to release a free patch for schannel to support it which is unlikely), MS would be rubbing their hands in glee as they'll look to businesses to move all those sites to IIS7.5 on Windows 2008 which does support TLS 1.1 and 1.2 already. Add to that the time to test upgrades, migrate applications, provision new hardware, and train staff to support another version of Windows, and it's clear that it's not a small tweak to turn this on. In an ideal world MS would release a patch for schannel on Windows 2003 to add this to IIS6, but I seem to have left my rose-tinted glasses at home.
Moving to open source might help (say using Apache 2 on nix with mod_gnutls, as mod_ssl doesn't support TLS 1.1+ yet), but the cost of moving from Windows to nix might be more than simply going to Windows 2008 - it all depends on the IT dept capabilities and whether applications can be ported. A free OS doesn't mean that there's no cost implications. Moving to Apache on Windows 2003 won't help because the Win32 port uses the Microsoft Crypto API for SSL/TLS support, and that doesn't have TLS1.1+. Catch 22.
Short term making stream ciphers (such as RC4) preferential in the Windows crypto settings, or in the case of Windows 2003 disabled the CBC cyphers (you can't set a preferred order, just enable or disable cyphers individually), eliminates this vulnerability at the server side and doesn't appear to break anything (at least not that I've seen as yet).