To be clear, that sentence was in there to illustrate the effect that single-bit errors could cause. That incident happened after Google had already long since switched to ECC and obviously wouldn't have been prevented by it.

However, we have a large number of other processes (testing, type systems, formal verification, code reviews, release processes, etc.) to protect against software bugs. There is no protection against cosmic rays. You don't want to be in a situation where all of the defect-mitigation work that the last 50 years of computer science has accomplished is rendered useless by a random freak occurrence.

(The bug in question was actually in a migration script, and made it into production because people thought that migration scripts were one-off throwaways that didn't need the same amount of testing, code review, verification, and general carefulness that the production code does. Lesson learned. The postmortem for it actually had the lesson of "Treat your migration code as permanent, and apply all the same standards of maintainability and reliability of it that you do to production code.")