However, the "no churn" requirement bugs me too. In startups, churn of some sort is usually inevitable and healthy: not only do start-ups fail and/or down-size, but there are also changes in direction and culture. Big companies, on the other hand, have frequently changing business objections to and a little flexibility: it's too easy to get stuck in a position where one isn't learning.
Perhaps Google's approach to this is in the right vein: use the hiring process to screen for people who are "smart and get things done" (with a high degree of certainty), yet allow them to change projects/groups at will. Reward accordingly for business priorities.
However: start-ups can't afford the costs of Google's hiring process and many big-companies can't attract the sort of talent where this practice would work. As such, churn (at least for engineering) is inevitable.
On the other hand, doing a background check and actually following up on the references, should filter out the "job hoppers": people going from position to position for a raiser or promotion. In fact an ideal test would be to initially offer someone coming from a short stint a slightly lesser compensation -- and then give them an immediate raise.