I quite enjoy reading lore. Even for games or settings I have no intention of playing. How much official game lore makes it into my games depends entirely on how I feel about the specific bits of lore and the style of game I'm going for. I don't treat lore as some sacred cow that must stand no matter what. All bets are off once the PCs encounter the lore; by definition they're supposed to be changing it. Or at least trying to.
I have no problem with major changes (be it a retcon or a the lore going forward as time passes) to a setting's lore IF it's done well. A good example of how NOT to do it is Legend of the Five Rings leaving it's RPG lore to be decided by the results of their card game tournaments. This led to, among other things, the Crab Clan being fooled into allying with the Shadowlands. For those not across L5R lore: as it stood (and theoretically still stands) this is impossible.
As to the "what's lore, what's game mechanics" side of the thread...
Most games have lore baked into their rules sets. I'd say anything except the most generic rules sets must have at least some lore written into them. I'd say that in DND across the editions it's a fairly light baking in. Colour coded dragons and infinitely regenerating trolls and spell names can all be changed without any serious change to the game. Even changing the source of clerical magic wouldn't necessarily change the game play.
Towards the other end of the spectrum games like Exalted or Numenera or Call of Cthulu have systems especially designed to give a specific feeling of play. It would be difficult (maybe impossible) to divorce the rules sets entirely from the setting. Exalted has spells, charms, powers, and other stuff (so much stuff, my head just started spinning about half way through the rule book and I had to put it down and go have a little rest) that are all intimately tied to the lore. How much of this can you drop and still call your game Exalted? I dunno, but I think most of it's required. (Full disclosure, I've never managed to play Exalted so I'm guessing here.)
Call of Cthulu absolutely has to have a system to represent ploughing through musty tomes and learning things Humanity Was Not Meant To Know. You could change the mechanics from (is it still the percentile skill system?) to some different game mechanic, but you have to have something to do this or the game loses a central piece of the experience.
Level of simulation is a completely different dial. Tic-tac-toe is a game with only rules, no lore, but it's not required to simulate nuclear explosions. (Well, except when a kid figures out that the only square that matters is the central one, and adults have just been humoring them all along.)
Don't forget, tic-tac-toe can also be used to avert nuclear apocalypses.
1h 54m | PG
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