Considering Windows XP is built on Windows 2000, I think microsofts response is very unreasonable
Yes, Windows XP is built upon Win2000, which in turn is built on Windows NT 4.0, which is based on NT 3.51, which has its roots in NT 3.1.
Do you think IE7 should be ported to those as well?
Do you really
think that no changes have been made in the kernel and OS between W2k and XP?
Each version - each service pack too, especially major ones like XPSP2, have made changes to the APIs. Do you want Microsoft to start backporting all the new API changes to W2k? How long do you think that will take? This is like releasing an XPSP2 equivalent
for W2k - an OS that's over 6 years old and has moved to Extended support.
You say that it's still a good OS and is used extensively? You're right, of course. Does that mean that Microsoft should still support it? Yes and no. Security and critical fixes should and will still be released - but to add new features, new APIs and support
for newer software? That's what XP is there for.
Trust me, I'm familiar with the time and money needed to move large organizations to a new OS. Many places, some of which I've worked in, chose to skip XP when it came out since it offered few benefits over W2k. That, however, was 4 years. XPSP2 isn't the same
beast as vanilla XP, and an OS that was "good enough" for 2001 isn't necessarily enough for 2005.