"Why do we hire you", what should be the answer to this question being asked in interviews?

Well, good question.
If I’m being asked the said question I would try my best to show my efforts, confidence to let the interviewers feels that I’m eligible or capable to have the applied job.
No one is perfect in this world and if “Confidence is the key to success” then I would say I'm adaptable and aim to be successful.
Having me in your esteemed organization you will gain a confident, hard worker, quick learner, motivated & professional candidate which will efforts to fulfill your company demand while I have been working in this field for10 plus years and having most experience in Business Administration line.
Moreover I would just say I do respect my work, give value to my work, having extra care in my deeds with proper judgment, having patient to fulfill my customer demands as well as to achieve the business goal.
The most important thing is that the position a candidate is going to be applied must have adequate knowledge on that, should have capability of work, quick learner, ability to work hard, shows his/her efforts that he/she would be an asset to an organization.
Thank you.
     

The interview is like selling your skills to the company.
Before going to an interview you should read a lot about the position you're applying for.
Having all the knowledge about it will help you to answer this question perfectly.
Meaning, you will use the job description and responsibilities and match them with your skills and professional experience.
By that you will show the interviewer how you will add to their company and at the sometime how you will benefit from them. 

Thanks guys, i agree confidence is the key to success...

Welcome to get benefits to achieve your goals

the answer of this question should give the interviewer two kinds of impressions, first, they should beleive that you will add much value to the company and join their team quickly, second, you should show also that you did your homework and informed about their company core values and goals, and you are interested in helping them to acheive these goals while you injoying the core values required.

because you will add value to this company

You should hire me, because , i have got great customer contact, and , i can make your business, 3 times more profit, what you are expecting, and also , i have studied your company product's what you are dealing with, and also you are based in all over the country.