When answering a question, the reputation points for "vote up" is the same for an interesting / difficult question or a simple question.
On Stackoverflow for example :
This is useful but it doesn't represents the knowledges of the repliers. Because the most of the people in the domain can answer this.
Generally a simple question is just a fight for "the person who give an answer fastest"... Moreover everybody rush to "vote up" in order to being agree with answer. So you will see simple answers with a hundreds of "vote up" and answers with true research and few "vote up"... For me, the reputation system doesn't reflect necessarily a truly knowledges on a domain.
There is a snowball effect on "vote up", because a person with lot of reputation will be covered of vote up for his answer. More "vote up" he has, more he will have. There is other interesting answers sometimes of people with less of reputation relayed to the end.
Why don't affect a number of reputation points in agreement with the "vote up" of the question ?
I doing my best to write a correct english, I hope this is comprehensible.