I think blaming bots just because you don't know anyone is shortsighted. There are a lot of possibilities... people using 4 year old computers and aren't computer savvy (this is very common) and people using what the IT dept set up, and they only allow IE and XP.
I do web development work that caters to auto dealerships, and nearly all of them are still using XP -- It was just in the last year that we've seen a dramatic drop in IE6 usage even though IE8 has been out for years. IE7 is currently tied with IE8 for the most popular browser used to access our site.
I just did some analysis on statowl.com and determined that 50% use IE and 30% of IE users are using XP then 15% of US-based internet users are using IE on XP. I did this little exercise because I wanted to know if I switched to SNI on my general server how many people would be disenfranchised.