Actually, I think this is an interesting lie for a different reason. Look at their no. 1 competitor, Google. They had a PhD in computer science as CEO and now a guy who well on his way to a PhD came up with an algorithm that, as far as I can tell, revolutionized search. Why did this Yahoo guy lie? Maybe he felt pressure to keep up with the Google guys, and thought a modest lie about a B.S. in Comp Sci would do the trick while going undetected. It might be sign of the times--that PhDs and PhD-equivalents are heading large companies. And a funny misread too--their 2nd foremost competitor in search was founded by a dude without a B.S. at all.

Addressing your other points: I feel like a CEO should be aware of how he/she is being perceived and correct any mistakes about his/her record.