Even if we assume that each page only loads a single ad, which either succeeds or fails, the perception of a site being unreliable hurts the company running it.

Even if we assume that each page only loads a single ad, which either succeeds or fails, the perception of a site being unreliable hurts the company running it. Household names like Disney and Sony might be able to live with that, but they'll still do everything possible to avoid downtime.