If they're including the dryer sheets with the machine, they can't void the warranty if you use 'em. That would be a huge lawsuit on grounds of consumer fraud, i.e. the allegation that WP was deliberately trying to trick people into voiding their warranties. Though what's really going on would have been the result of lack of communications between the manufacturing dept and the marketing dept. Chances are if this ever happened, some WP dealer would spot it immediately and raise holy hell with WP over it, and that would get it stopped in its tracks.