Well, I may be wrong but since noone answered (well, since I started writing this) maybe someone can comment on my answer as to what they think too. :)
What are the kinds of differences between small and little (usage etc)?
-this is less direct (more soft) and allows open discussion. It is not expecting a very direct answer such as "yes", "no", "good" or "bad".
What is the difference between small and little?
-this is more direct and blunt. The question is expecting a more direct answer such as "small is a, and little is b".
A lot of words in Japanese are used not because they are necessary to communication, but instead because they convey the feelings and intentions of the speaker when speaking. Actually that is quite similar to many of the words in other languages writing. It just sounds better, I am sure when you translate these sentences into English you can also feel the effect even though they are no longer in Japanese. I think the reason this use of filler language is more stressed in Japanese than in most languages is because of the culture, although I most certainly have gotten annoyed at people in the past whom were clearly not native English speakers but did not make use of words such as "please" and "thank you"...but Japanese language takes it further than this where simply adding "please" or "thank you" cannot make up for lack of filler language (while in many cultures people will find it acceptable to be a little blunt if you add some polite words in as well).