Red Ring of Death" accounted for 60% of hardware failures it's documented and supposes that figure could keep growing. "It is reasonable to believe these failure rates will increase over time, since the Xbox 360 failure issues tend to increase with prolonged use where overheating appears the main culprit," SquareTrade CEO Steve Abernethy told 1UP.
Admittedly, SquareTrade does not track specific versions of the console, but it's fair to assume, as Abernethy does, that "most, if not all" recorded hardware failures have occurred with the original Xbox 360 motherboard. Microsoft openly acknowledged these defects (and has apparently improved the design of the console versions currently on the market) when it made a costly, but necessary extension of its Xbox 360 warranty last summer. True, the Xbox 360 failure rate may continue to grow in the short term, as more original units start to glow red, but it could conceivably shrink in the coming years as the revised hardware install base overtakes the original population.
1UP also notes that SqaureTrade's reported Xbox 360 failure rate may suffer from a lack of randomness within its sample pool. That is, frequent console users are more likely than casual users to seek out the services of a warranty provider, and are also more likely to experience hardware failure due to overheating from constant usage; thus, SquareTrade's samples are likely skewed by a disproportionate number of this user type. This doesn't discredit SquareTrade's findings, but it serves as a reminder that an absolute measure of Xbox 360's failure rate is difficult to determine.