I'm pretty sure he didn't mean everyone had to share the same red shirt, passing it on between presentations.
I for one would not have liked to wear it after Ballmer.
This is something that MS makes you do when presenting at conferences (it a uniform rather than the same actual article of clothing of course)
Scott Guthrie's red polo short always made me chuckle, he wore it without fail on stage. And then at one conference the whole audience turned up in the same red polo.