A) People who are scattered around the world dont always get a chance to get startup tees at events. 40% of our shirts are shipped internationally. They love feeling like they are a part of the community even if they are overseas
B) We ended up trying to add more value to each package by adding in not just a shirt but stickers, discounts on services, etc, to make the value of the bag much higher than what they are saying. (Heck, I even lowered the price after I saw HN comments a while ago about another service that was similar)
C) We dont do any logo shirts, so that they were exclusive to the site and were interesting enough to wear outside of the startup context.
The combination of these things definitely helped me keep some of the subscribers we have had and they seem happy.
This is a cool idea, hope the YC tees takes off! I'm subscribing for sure :-)