Not the IDE, the project. It's conceivable that someone would use an old IDE (they're comfortable with it, they paid a ton of money for it and can't be bothered to upgrade, etc)

You're right. I use VS2005 because in my daylife job I work mainly with industrial Windows CE 6.0 projects, and Platform Builder is a VS2005-only tool (why, Microsoft?) so I'm somewhat forced to keep using this version. Just as the blacksmith that fixes everything with a hammer because he is proficient using it (despite not being the most suitable tool in all cases), I use VS 2005 for everything :)

There's another reason: any newer VS version can import projects from older versions, but the opposite doesn't hold true. So I'm not leaving anyone out.