The objective for descent planning isn't to achieve a 3 degree descent path. It's to achieve the most efficient descent for fuel and time adjusted for altitude and speed constraints. In the MD80 you had to figure the stuff out. Modern jets, with modern FMC's, are more capable than the overwhelming majority of pilots. I've yet to see anyone grab a calculator and start comparing the descent winds to do the math the FMC does without having to ask it.
The 'rules of thumb' are for the old school flying or non FMC aircraft. They're a good back up, just like the 'trust but verify' aspect of FMC use, but the primary method to achieve efficiency is via the modern tools provided. Updated winds are a key component of the FMC's computing ability.