Strange. I've played since the mid-90ies, across all kind of groups, systems and editions, and this never came up. You consider it an essential element of D&D, I've never seen it. And I've never considered it missing. It's kind of funny because you talked about houserules and optional systems, but then you complain about an element that you miss, and never thought of adding that yourself. (Especially since stuff like wandering monsters are easy to add without changing core rules)In other thoughts: 4E gimped the exploration element of the game by removing resource management as a game play element. Exploration always has a timer attached. Wandering monsters. Lair reinforcements and new traps. Etc. By removing a timed element you gimp the Cause & effect play of explorations. Your actions no longer have consequences if you don't have to worry about resources.
I think that above all the niggly details of whether Paladins are LG and what not, this will be the core difficulty of uniting the player base. It's not that different groups play (and like) different editions, it's that groups play what boils down to essentially different games.
Some play an open world game, where the group explores a continent with wandering monsters and trap-filled dungeons. The next group plays a soap opera with occasional fights. The next group plays a tactical wargame. Another group reenacts the first Alien film with swords and spells instead of guns. Yet another group is in a gory shonen manga. And it's all D&D, and even the same edition.