Historically, the coupe has always had larger audio systems on the lower trim levels in comparison to the sedan. I think it has to do with a price discrepancy in manufacturing, the coupe is cheaper than the sedan to build, so in order to align their prices more closely the coupe usually ends up benefitting from larger audio systems on lower trims as well as larger wheels. For instance, the new Coupe in LX form comes with the EX style rims. However, the coupe also has no EX trim, instead it has a LX-P trim.
Honda rehashed the packaging of the coupe to meet the demands of the coupe buying audience which cares about style and niceties like audio systems more than sedan buyers, so it makes total sense from a marketing standpoint that the coupe be packaged differently than the sedan.
So it's totally possible that the coupe EXT and above could get the 450 watt system (i hope so, since EXT is exactly what i want!)