i agree that the route one takes for a ride is probably the most important aspect of a commute, but there is a massive difference between a 50 dollar and 5000 dollar bike: Reliability, comfort, fun factor etc...(and i commute on a bike I built for under $100). If someone can afford an expensive bike, let em buy it. Who cares? If anything it just injects more money into the bicycle manufacturing industry and that can't be a bad thing.
However, yes. The route affects ride quality more than the bike. But once you find that perfect route, what better to share it with than a sweet bike?