It's all about competition. Obviously the motor is the most important component. That being said, in a race where everyone is a pretty solid cyclist, you're going to want to utilize every possible advantage that you can. TT bikes, aero helmets, aero wheels, light carbon frames, the position of your water bottles, hell even the decision to wear gloves all have some impact on your drag. Add them all together and that impact is significant. We're talking 50-60 seconds in a 40K time trial. Over an Ironman bike leg the impact is huge - maybe 3-5 minutes. It doesn't sound like much, but if you're gunning for a spot on the podium, every second counts. I would like to know that if I have to hold 22mph for 112 miles, I am cheating the wind as much as possible.
Sure, there are "freds" out there with all the most expensive equipment that couldn't go fast if you threw them off a cliff. I pass guys like that all the time.
I have also been schooled by dudes in cut-off jeans on a 30 year old steel frame single speed. There's always some one out there faster (and slower) than you. I like triathlon, because it is also an individual sport. In the races that I know I have no chance of making the podium, I can still compete against myself - trying to get the absolute best performance out of my hurting body.