[pokernicus]

I can think of several reasons why you might want to call in such spots. First, you'd gain potentially useful information about your opponent's betting habits. Second, in heads up play Ace or King high might actually be the best hand -- especially considering that David may well be bluffing. Third, if you do call with hands like Ace or King high, you might deter your opponent from bluffing in future hands (since you've established a willingness to look him up with relatively weak holdings). Fourth, you may have picked up a possible tell on your opponent, and you'd need to see his or her hole cards to verify it.

Also, one thing to keep in mind is that (especially) in heads up play, you have to look at the hands context. If you study a single hand in isolation, the play may make little sense -- but it might be appropriate given all the hands that have been played and, perhaps, how you might be setting your opponents up in future hands. Even though the play on a single hand in isolation may be 'sub-optimal' it may lead to better overall results for the entire session.

Also, you're only seeing a small fraction of the hands anyway, which makes it all the more difficult to figure out what the players might have been thinking.