A few weeks ago, a current student who sat on a panel at a program for prospective students told me about the day his UVa decision letter arrived. He came home from school and opened the mailbox to find a thin envelope with a UVa return address inside the box. Upset about seeing the dreaded "thin letter", he closed the mailbox, went inside his house, and went to bed.
Later on, one of his parents came home and asked why he hadn't read the letter. He didn't see a point in opening the envelope, but he did...and found our congratulatory letter inside.
ALL of our decision letters are sent in simple envelopes. That thick package comes a little later. Mailing a simple letter has a few purposes. First of all, it's faster to put a letter in an envelope than to put a fancy package together. Second of all, a regular rate letter probably travels through the mail system faster than a bulk rate package. We're opting for speed over ceremony, as one of my colleagues says. We'd love for all kinds of bells and whistles to accompany your decision letters, but the fact is that we all want those letters to get to their destinations as soon as possible.