So I am curious.
Who here would claim that they play ANY TTRPG 100% rules as written with no alterations or omissions? House ruling things not covered by published rules would be allowed but if there is a rule for it, you have to use that rule 100% unaltered for a situation it applies to. 40+ yrs in the hobby and I know I never have. I suspect it can only really be possible for games that have properly minimalist rulesets. But let's say any edition or incarnation of Dungeons and Dragons. Have you every played it 100% straight up RAW with no alterations or ommisions?
I've played loads of RPGs RAW (certainly no knowing omissions obviously there are known omissions and unknown omissions).
I'm surprised that you don't think this happens.
Though not as surprised as I was by the title I admit...
Will we still be playing 100% un-altered rules 20+ sessions into a campaign? Harder to say, but like, let's look at some kinda random examples:
1) WEG Star Wars, DarkStryder campaign - We certainly played through the first book of the campaign (at which point the DM gave up for unclear-to-this-day reasons, I suspect not really game-related) absolutely rules-as-written (I don't think I can ever write "RAW" the same way again, you scoundrel!).
2) Daggerheart - So far, we have no reason to change or modify any rules beyond the ones suggested to be modified by the campaign setting, which I don't count because the game said so. If I think of anything we've changed I'll add it.
3) 2E AD&D - We played it a lot more rules-as-written than a lot of people did, primarily because I was exposed some other people's house rules early on, pages and pages of them, and they were, even to me at 11 or 12, obviously mostly drivel and showing in many cases (and this is something I often see with house rules) that the people writing them just didn't understand the existing rules. But we definitely used a lot of optional rules and certain "takes" on some rules which I know were not the conventional take, and I don't think we used any of the default rolling chargen rolling methods for long. Players Option kicked in later too. I'm not quite sure what would count as rules-as-written in the very complex rules-environment 2E was in but we certainly weren't playing it 100% that way, just a lot more that way than most. 2E was also the most "fudging"-necessary-feeling RPG I've ever run.
4) Cyberpunk 2020 - I do not think we changed or omitted any non-optional rules, though we certainly interpreted some. Still, pretty close to rules-as-written I'd say.
5) Shadowrun 2E - I know we had some house rules in SR2, because some stuff just didn't work right, and I discussed it a lot on the old Shadowland.org (ah bygone days!) messageboard, and people had some good fixes and adjustments.
6) 3E D&D - We used quite a lot of house rules and optional rules because frankly 3E kinda sucked hard rules-as-written in the base books.
7) Spire - I actually made several rules changes after a couple of sessions, which made it more like Heart, in some ways, mechanically. I did run them by the game's creator on the Discord and he thought they made sense, so there's that.
I could go on. I would say if we play an older game eventually we'll come across a rule that's either mechanically broken or just doesn't improve the game and we'll likely change that, but I think whilst I'm very much in favour of people feeling enabled to change rules, we don't often do it.