Digital Foundry talked to Darren Thickbroom, an engineer for an independent console workshop, who offered a lot of revealing insight into the issue.
Thickbroom explained that the massive amount of heat generated by the HD systems -- exacerbated by high-end technology crammed into a small compartment -- contribute to their eventual demise (and all because you played on them so often). And like many "exclusive" games this generation, this is by no means constrained to one console. Though Xbox 360 failure rates are abysmal, Thickbroom noted that more PS3s have been appearing in his workshop. His gloomy prognosis? "It comes down to how much you play it. People might disagree with us, but this is the way we see it: if you handle the machines day-in, day-out with the issues they've got, I'd expect to change them every year."
We have the same rule for our underwear, so that part should be easy to remember.