Right, there is a reason newspapers long ago realized multiple columns is better than full-width text. Imagine reading New York Times if it had only one full-width column. People would stop subscribing to it.
it what's also nonsense is, to firmly associate browser window width with tab content width. The user can control these independently. Maybe it should be made easier to do so, or more comfortable. At some point though we should take a step back and ask ourselves how we can solve the problem without dumbing down the interface so much, that capable users suffer.
I seriously doubt there are any people who resize their browser window every time they switch tabs.