Practical tests aren't the only judgment / hiring criteria. There is a lot more to getting through an interview than a cert test. Part of it is social skills. Part of it is whether or not the candidate is honest about their abilities. Part of it is past experience. The cert test only plays a part if the company wants a cert or if the person is coming from a non-IT background (like me). And a lot of interviewers will make the candidate solve real life problems to verify that they have the skills they claim to have.

Answering those questions the way you are proves to me that you don't have the RL experience I'd expect someone to have. It's one thing if you come to me saying "I only know what I learned in my home office setup." It's another thing if you're telling me you know from disaster recovery and backups and then give me THOSE answers. Because then I know you don't know what you're talking about.

EDIT: I should note that a lot of us who are involved in the hiring process are okay with the prospective employee saying the words "I don't know, but I can find out" or "I don't know, but I can learn that." No one knows everything and we expect there to be gaps, especially if it is a junior DBA position. It's someone coming in and acting like their skill level is a 9 (on a 1 to 10 scale) and only having a 1 or a 2 level ability that bothers us.

If you learn the material (do your research well) and practice it with a Dev copy of SQL, you are ahead of the game. If you are honest about what you can do and what you've only read about, you are ahead of the game. The days of faking one's way into a DBA job are pretty much over. Someone doing that might still get a job, in a one-DBA shop where they have to handle every crisis, including basic server administration. But not in a bigger environment where managers have learned to recognize the experienced from the non-experienced candidates.