Ah, now that I have seen an explanation for. They're trying to avoid hanging the PMU. (The PMU is a computer. It can crash, too.)

I think maybe their reasoning is that, each time you reset the PMU, there is a slight risk that it won't recover properly from the reset. The symptom as described in, for example, http://docs.info.apple.com/article.html?artnum=95037 is:
Quote:
Important: Be very careful when handling the main logic board. Remove the battery when handling the logic board so the PMU is not affected. The PMU is very sensitive and touching the circuitry on the logic board can cause the PMU to stop responding. If the PMU stops responding, the battery life goes from about five years to about two days if the PMU is not reset.
I would imagine that, however unlikely that might be, Apple surely gets a few service calls on it, and they're tired of having to pay for the repairs (even if all they spend is lost goodwill to the customer whose computer they refuse to repair under warranty).