[cynwoody]

You are mistaking an attack on the Web browser with an attack on the OS.

A successful attack on a Unix user's web browser can still do plenty of damage. It takes root to rm my /bin/ls, but I can fix that easily without a backup. However, an attacker needn't be root to rm -rf ~, and I might not have a backup. Plus, some of that stuff might even be confidential.

[zeugma]

However, an attacker needn't be root to rm -rf ~, and I might not have a backup.

If you don't have a backup, you obviously don't care enough about your data for it to matter if you wipe ~/*

There are plenty of really painless backup programs out there that you  basically fire and forget. I use 'backintime" which works a lot like "time machine" for Mac. I can recover any file that has existed on my computer for over a year if it has been on my computer for 24 hours.