By the very same logic there is no reason (apart from investing time & money) that Firefox shouldn't be able to run on 16-bit systems. But you don't see anyone complaining about that.
You have to draw the line somewhere. XP is old. There are a lot of decent OSes and upgrade-options out there. I see no problem ignoring XP for any new, major development projects, especially if new APIs will need to be developed in the process.
There are millions, possibly a billion XP installs out there (I'm one of them). They can run all the newest software still, it's 99% the same API as Vista and W7. Plus XP is still faster than Vista or W7, uses less memory and FAR less disk space to do the same functionality.
Don't confuse the need to sell more software with the previous version not actually being outdated. There's a huge difference between Windows 3.1 being extinct and XP.
Good for you. You are obviously a power-user and any restriction placed on MSIE will not really affect you as I assume you are using some other browser anyway.
The fact remains that XP is almost a decade old, and just because your OEM paid $20 for XP 9 years ago, does not entitle you to having free support, patches and new APIs backported to XP forever.
Microsoft has officially ended regular support for Windows XP and are now only providing patches/bug-fixes while on extended support until 2014.
Windows XP might work for you, even under these conditions, but don't delude yourself into thinking it isn't outdated just because it works. When the vendor stops supporting it, it is outdated.
Unless you are running on a machine with less than 1GB ram, I see no reason to cling on to XP.
You have to draw the line somewhere. XP is old. There are a lot of decent OSes and upgrade-options out there. I see no problem ignoring XP for any new, major development projects, especially if new APIs will need to be developed in the process.