Should all testers be developers?

One more QA manager interview question could help to analyze the management abilities of candidate for QA manager position. This interview questions especially critical for the QA teams working in Agile environment.
In certain domains, there is some amount of testing that cannot reasonably be automated in the proper time. This testing requires that QA Engineer eyeballs carefully look at the screen and work through the application under test. It isn't necessary for these QA Engineer to be developers, in fact, it might be better if they aren't programmers, since developers view the world differently than most people. You may want non-programmers QA Engineer for the following mundane tests:

• UI testing
• Usability testing
• Internationalization testing

In the same time QA Manager definitely wants your testers to have the coding skills and be developers when doing the following kinds of tests:

• White box testing
• API testing
• Performance testing
• Database testing