Maxperson
Morkus from Orkus
In one case it's a roll versus a score (attack roll versus AC) and in the other case it is also a roll versus a score (Stealth roll versus passive perception). There is no difference!
So when I go to a DM and tell him that I want to take my +10 to hit and automatically hit all ACs of 20 or lower with my passive aggressive, what do you think the answer will be?
You might as well complain about the 'perfection' of the guy's AC (he has 'perfect' defence of 20 and any attack roll less than that misses 1 million times out of a million!) or the 'perfection' of the DC to save against a particular caster's spells (he has a 'perfect' DC of 20 and any save less than 20 fails 1 million times out of a million!).
It's not the exact same situation. AC and a specific spell are both very tightly focused in both scope and area. Perception is not.