Makes sense to me. Lower engine speed should mean less stress--the torque convertor has more slippage at lower speeds. In park/neutral the output of the convertor (turbine?) is spinning, while none of the guts are--and those guts won't be spinning until you start moving.
Maybe shifting into neutral would help, depending upon if the pump runs in in park or not. A bit more loading, to bring engine speed down, that is.
But it seems pretty easy to find things to do while killing 30 seconds--like buckling up, checking windows/mirrors, etc.
2011 Toyota Camry, base, 6spd manual, 95k, hers
2010 Toyota Tundra double cab, 4.6L, auto, 96k, his