I believe you are misinterpreting the meaning of the sentences. Thus, the question represents a misunderstanding, rather than a difference.
Question 1.a: the question is being asked of the general audience, which would include the speaker.
Question 1.b: is being asked in a more directed fashion, with the object being "you".
When you look at the phrasing this way, it becomes apparent that, in question 2, precisely the same thing happens. In 2.a, anyone in the speaker's audience, including the speaker, can answer the question. In 2.b, the question is directed specifically to "you". It is not asked in the question, but it may be helpful to realize that "you" may be singular or plural, one or many.
Also, the first style, where the speaker asks the question so that they can also provide an answer, is frequently used as a rhetorical device. In that case, the speaker knows the answer, or believes they do, and is seeking to make a point, or to direct the audience's thoughts.