Frankly, I'm sure Deloitte had absolutely no intentions of prematurely inflating your hopes only to depress them, but it's a part of the process. Your resume speaks to your education and your experiences, but they have to interview you to get a better understanding of how you react in certain situations. On no levels do they ever promise you an offer after an interview. If they were going to promise you an offer, what would be the point of the interview?
Secondly, I wouldn't ever discourage anyone from applying to Deloitte. It's an amazing firm that works incredibly hard to make sure that the people it hires fit the firms goals, culture, and overall mission. People are Deloitte's most important asset, and ensuring that the people they hire "fit" is of utmost precendence.