Tons and tons of developers and plenty of DBAs still believe in not hooking yourself to a single vendor. I interviewed someone just a little over a year ago who lectured me on my technical questions because they were too "Microsoft & SQL Server specific." His argument was that only lowest common denominator SQL should be used so that it's easier to port between database systems. People really do still believe this.
Agreed, people believe lots of things, but that doesn't necessarily make them relevant, or the best way to go. Like I have said to many customers in the past without reservation. "There is what you want, and then there is what you end up getting." and my boss backs me on it every time too. Our business is still thriving. As far as the interview goes, you are asking the questions not the interviewee. You can ask anything you want within reason to satisfy your need to assess his/her specific skill set.. :-D
"Technology is a weird thing. It brings you great gifts with one hand, and it stabs you in the back with the other. ...:-D"