I take it you've never done support or tried to fix a users issue?
Trying to find out what browser and version a user has can often be like pulling teeth if they're not an experienced internet users; being able to link them to a page and get all the info you need without a miscommunication is a godsend.
This is a genuine question, I have no idea why this seems important/interesting enough to be No 1 on HN.
What am I missing?