Thanks for clarifying, VirtualAce. My point was most of these questions are repeated in many interviews (especially the one about strengths/weaknesses). They are so common that it would NOT be in the best interest of the candidate to be unprepared for such questions. So it would be folly on the part of interviewer to expect any candidate to answer honestly to these questions. So these questions, in a way, indirectly measures the ability of the candidate to lie rather than whatever the interviewer is really interested in.

Here is a funny post on Slashdot that I found on the topic:
I actually did this once (did not get the job, despite being recommended by a friend who worked there):

-Name three of your strengths.
-Well... I'm honest and... let's see... I'm reasonably quick to spot and diagnose flaws in any given system... and I'd say I'm creative.
-Good. And do you have any weaknesses?
-I'm a liar.
More such gems at Blowing Up a Pointless Job Interview - Slashdot