I've noticed that the possible reason for this may be legacy software, software that may exploit some security hole in Internet Explorer 6 in order to operate. At my last job, I downloaded Internet Explorer 7 because I thought it would be more secure while I was performing research. (At my new job, the IT department is much more serious about security, since the company deals with health care data. I am unable to modify much of anything. My screen resolution isn't even permanent!)
When I tried to access one of the company's intranet pages for storing customer information, I received numerous errors while trying to use some of the features. I tried lowering the security settings, updating all sorts of related software, and modifying the connection settings, all to no avail. It just wasn't going to work on Internet Explorer 7.
The software has some serious flaws - it's number 8 on the worst tech products of all time rated by PCWorld and the Computer Emergency Response Team has recommended that internet users not use it at all. So I'm wondering, with all of the security flaws and out-of-date features, why do companies still use it? Do newer versions lack compatibility with legacy software? Is it too difficult and time-consuming to convert to the newest version? Is it easier just to wait until Vista is the defacto operating system for business PCs? What is the reason?
Update: One of my co-workers had IE 8 installed. It was an attempt to help a web interface work better, and it seemed to do the trick! Lesson: Upgrade!