I don't fully agree, there is a reason chrome and firefox all auto-update nowadays. To make the web better and faster for everyone, if you find that 1 in a million people who are still using IE7, No I personally don't feel I have to spend x hours to make the website just for that one person.
But that being said, I do feel we must make the web more accesible and love your write-up about how we can achieve this. So no attack here, just wanted to state there is a grace field we have to keep in mind.
Effort vs Reach (I do work for a corporation who is strict on hours)