Any Whirlpool dryer manual states the service quote. If you would follow these, you would have to call a service technician every 5 years. And, honestly, who does that? (Except of those who do it themselves, of course.) It's just a phrase put there so WP could say, if a dryer starts a fire, "Did you have it cleaned? No? USER ERROR! Your problem."
As the dryer is ventless, and you stack it, as long as it is free standing, you can just install them with a 1-2 inches more space to the wall. Then, every now and then, just take the brush attachment of your vacuum, put it at the end of an solid extension piece and you should be abled to clean it fairly easy without moving the dryer.