It's one possible method, although there are certainly others. As another example, in a cash balance plan, you might prorate the contribution in proportion to the hypothetical pay credits.
I'm having some trouble understanding your claim that sec. 412 is not related to the individual benefit calculations. 412 says that for a single employer plan, the minimum funding standard is determined under sec. 430. 430 says that the minimum required contribution is equal to the target normal cost (plus a shortfall and/or waiver amortization charge, or minus the amount of excess funding). The target normal cost is equal to the present value of the increase in accrued benefits for the year, plan-related expenses and mandatory employee contributions notwithstanding.