Today in class we were talking about Professors. I don't see what's the big deal about them. Most of them did graduate classes, which are not that hard, and then did a research project to finish their phd. However, I don't understand why Professors should be talked with a such respect. I bet apart from the 10%(who do world changing research) most of them are average at best as teachers and as researchers in their field. I don't even get why some professors feel they are so important that TA's need to hold office hours on their behalf. 

They're there to teach you thus are deserving of respect. That and they have documents you don't have but you want and in order to get these documents, you need to go through them first.

Teaching in general should be held in higher respect in the US (as it is in some other countries). Unfortunately, there are a whole host of reasons why that isn't the case, including the presence of a lot of teachers who aren't very good at teaching.

I don't know about where you live, but in Norway you have to study and do research and write fo a total of 7 years to be a professor. That's a lot in and of itself. Second of all, maybe it's just the thing that they devote their life to science, to always learn more? You say "aside from the 10% that to world changing research" implying that that's the only research that matters. Yet at the same time I'm sure you have a lot of respect for Stephen Hawking right? Even though none of his research is world changing. It has no implications on our daily life, and likely it never will. All it does is help us gain knowledge about the universe we live in, which is valuable in and of itself.

I think everyones has to be respected, being a professor or not. What I don't get is why there's so distance between them and us. Some of them are quite arrogant, I can give you that. I believe in a more familiar and close educational system.

You should try asking that question to your professors, you can get all sorts of reactions so it could be fun

Most teachers in the US (and yes professors that's what you are and I'll call you "Mr." too) are quite full of themselves and think of their profession as above all others. There are a few great ones that I've had that are deserving of reverence and I give it then. Most are ordinary and deserve the base respect of any professional to make the class run smoothly. When I got to college I didn't notice a jump in intelligence so much as a jump in arrogance and pushing of liberal political agendas and presentation of extremely biased viewpoints when politics were brought up.

One should be deferential towards anyone
RespectLove&pece xoxo

It's probably to make up for how small most teachers' salaries are, even at a university level.

To answer the headline: because they control your grade.

To answer the final question in the OP: because 95% of professors don't want to deal with undergrads, but are forced to as part of their employment. Having dealt with and been an undergrad, I 100% understand that attitude.