It looks like, after Microsoft discontinued WordPad, they want to implement more features into Notepad. If you want simple plain text editor you have to use msedit[1].
You can still open the real notepad, you just have to turn off a "feature" that makes running notepad.exe open the new notepad. Its called "execution alias" or something like that.
I just use the winxp wordpad.exe. (and calc paint notepad, and I use paint shop pro 4.12)