When you are an Australian OEM system builder and actually get one of these shirts, I bet it will arrive in shrink-wrap with a big EULA sticker on it that reads something like:
When accepting this EULA you agree to proudly wear this shirt to your work, to wash it daily using Microsoft(r) certified color washing powder (order no. X87-00640KB), agree not to remove or add any letters, numbers or graphics to change the text and/or graphics on this shirt and agree not to install Windows XP(tm) onto any OEM system again.