Microsoft doesn't care that you know how to change it.
They know full well only a tiny percentage of users will change any defaults whatever - the majority because they're afraid to. I used to see a fair number of machines that still displayed Windows 98 install welcome message because people were afraid to click the little check mark off.
Most of the Windows XP computers I see out there still default to MSN as the default home page, not because the users want MSN but becsause that's the way it came. I routinely switch them to Google because MSN takes too long to load when I'm working with the computer - once changed to Google they stay there forever.
The site and the ability to turn off (at least the obvious part of) the search feature is so they can point to it, just as you have, knowing full well it doesn't matter.
