I think I read back during 1.0 release that the choice to allow maps to reset when you portal away had something to do with performance, but that options where being looked at. I just want to reiterate that it is still something that I find jarring.
During the leveling experience, it is odd to portal to town to vendor or stash away loot only to come back and see that the map is reset. If you are lucky you were standing next to a chest and now you get a free chest, if you were unlucky you left an unique item on the floor and came back to find out the mob you killed is alive and took back his loot.
At endgame it can also suck at times, imagine triggering multiple prophecies and then having to abandon most of the loot cause your inventory is full and you can’t portal out.
Regards,
from a chronically casual gamer