First of all, not everyone can afford authentic jerseys ... some can barely afford a ticket, and would rather invest that money into attending a playoff game instead of buying a jersey.
Some people, for their own reasons, don't buy jerseys or even like them anyway. To say that "real" fans are somehow above wearing t-shirts, or that only "fake" fans wear them, is absurd.
What you wear has absolutely nothing to do with how much of a fan you are ... that's the kind of "elitist" garbage that we need to rise above, not encourage, and let people celebrate this team in their own way, whether it coincides with ours or not.