Silly young people and their idealistic, alternate world scenarios. T-shirts and flip-flops. Pfft. Next thing you'll be complaining about is "Why can't I just work from home?" and "I"ve been at this company for TWO MONTHS; how come I don't have a week of paid vacation?"
The American standards of professional dress and appearance dictate a tie and jacket (not necessarily a matched jacket/pants, but that's preferable.). It just give a more professional image. You have to look the part too, not just be good at what you do.