Honestly I can see good reasons for a lot of them. A bit of background, I do have a degree in business management as well as over 10 years experience. Some questions are used to throw you off your game...interviews have gotten to the point it is pretty much "memorize these answers", throwing an unexpected question allows you to see how a candidate acts on their feet when faced with a problem they didn't see coming. Others get candidates to answer things they may not normally answer.
For example, asking why you didn't get a 4.0 can be quite revealing. A good, honest answer would be, "I am a bright person, but I am not perfect, I got a 3.0 through hard work and 100% effort, it was the best I could do.", a trap you may fall into is "I didn't apply myself fully" which can lead an interviewer to see you may not always work your hardest at something...unless it has been several years, in which case you could follow it up with "I was young and didn't value the importance of hard work and a solid education, since then both my work ethic and real world education have increased tremendously" followed by examples from previous employment.
For the three things that would make you refuse a job. We all have needs, demands, and value different aspects. For example, I am currently an assistant manager and was a store manager of a relatively large retail chain (about $1.4 million annually in sales at my store). If I were to be asked that question when looking for a promotion now I would say that I am not ready to take over one of the busiest stores in the district...that while I may be interested still, I think it would be best to develop my skills more at a small to medium size store. Or if asked about a district manager position, I would explain that the pay could be an issue. I would break this down with a series of facts. For example, I would state that I know the highest paid store managers in our district make about $1000 a week for a 50+ hour work week, or $20/hr. As a district manager I know I would be on call 24/7 and would be putting in at least 80 hours of work a week. I would need to make $25/hr for the higher level of responsibility, times 80 hours, I would need $2000 per week.
The other one I love is the "why should we hire you". Even as an account executive, part of your work is in sales (albeit a bit indirectly). This question I am essentially asking an employee to sell themselves to me. The bottom line is employees are commodities, and just like any other commodity, a salesman needs to know how to sell themselves. The reality is if you can't sell me why you are the best candidate for a job, you can't sell my product to customers, or at that level, sell the quality of our product to the employees under you who will be selling the product.
There is no genuine justice in any scheme of feeding and coddling the loafer whose only ponderable energies are devoted wholly to reproduction. Nine-tenths of the rights he bellows for are really privileges and he does nothing to deserve them. H.L. Mencken