Some people, regardless of yearly mileage, are into having nice toys. Brand name may not matter to everyone, but I've been on club rides with guys who put in 2000mi/yr at the most, and they're rolling on $5000+ worth of equipment. On the flip side of that coin, a guy in my rando club rides a beater lookin' singlespeed conversion 1970s Peugeot and puts in over 6000mi/yr on it.
For my brevet/commuter, after suitable engineering I admit that brand selection is the next consideration. There are plenty of less expensive components just as suitable for the task; but Dang, my bike looks pretty.

You should see the starting lineup at any of my club's 400 - 600k events; it looks like a NAHBS showcase lineup... Pereria, Boxer, Rodriguez, Davidson, Steve Rex, Thompson, Calfee, etc. Do riders need a $3000 custom frameset to finish the ride? Heck no. There's more people rolling on Trek, Specialized, Giant and Surly bikes. It's all about riding what makes you happy. Some days for me, that means hauling out the 80s beater singlespeed conversion. Other days it means the fancy bicycle.