Sorting algorithms in general aren't constants, though. The implementation can have significant impact on running time, memory use, etc. And there are an infinite number of them with various tradeoffs you can tune.
I wouldn't expect an interviewee to know sorting algorithm X because they may just have forgotten. But why wouldn't they be able to come up with a sorting algorithm, and have some feel for the behavior? Seriously, selection sort is about as easy to come up with as fizzbuzz. If they can't think through a simple problem and come up with a solution, is it wrong to question their problem-solving skills?
Actually, if you asked in an interview how to sort, I'd try to come up with quicksort or mergesort. I wouldn't give you insertion sort or selection sort because I'd feel terminally embarrassed to go with so bad an answer.
Is it terminally embarrassing to say "this is bad, but..." and pass the test, then discuss (maybe write out) more advanced options? If all they care about is selection sort, you've saved time (often a good quality). If they care about more, you've demonstrated something, and opened the door for more.
I wouldn't expect an interviewee to know sorting algorithm X because they may just have forgotten. But why wouldn't they be able to come up with a sorting algorithm, and have some feel for the behavior? Seriously, selection sort is about as easy to come up with as fizzbuzz. If they can't think through a simple problem and come up with a solution, is it wrong to question their problem-solving skills?