1. Really not accounted for. If you had to use something to represent poor braking on the stop but little effect on the go, ice or packed snow from the "standard" contamination options would be your closest equivalent, but bitching at the airport authority would also be good.
2. Taken account of. Where we have a spoilers lost case that makes the emergency descent case not achievable with available pax oxygen, the procedure requires descent to a low enough level to assure the descent. In many cases it may not be required because the aircraft has margin to start with and you are just eating into the margin.