Getting the print to stay on Rashguards is not easy. You can't screenprint in the normal way because it will crack and peal on the rashguard material. We pretty much finally got it down pat but every once in a while we will have a shipment that we have problems with. Since we guarantee all "Authentic" Gameness products under normal wear and care, we are very picky with our products but even with that in mind, sometimes things still get messed up!
HCK used to sell rashguards that were sublimated therefore the print would never come off. The problem was it was very, very expensive to do this, thus his rashguards were $70.00.
I have not personally seen XFGear's rashguards in person, but from what I understand, I think they probably have the print down to a science. If they are actually putting the dye into the material instead of on top of the material, which is very close to sublimation, they probably can guarantee the print will last for years.