A cheap road bike will fall apart after a few hundred miles.

I think the reason that a good road bike costs so much is because road bikes are designed for thousands and thousands of miles, not a couple hundred miles before gears spin off the hub.

(for the record, both of the $200-300 bikes I've owned are basically in unrideable condition after a couple hundred miles).

Ask yourself, what's cheaper...

A $300 bike that falls apart to be replaced by a $1200 bike, or a $1200 bike?