Great point, that all makes sense to me!
I don't think it's a language thing, it's just people wanting more power rather than less. Any multiplayer PvE game forum always has a post complaining about nerfs being wholey unneccessary when they happen, and claim that players should only ever be buffed. Never mind the balance of the enemies and other systems in the game that would need to be adjusted to the ever increasing power level lol
In the case of your post, I think that allowing sneak attack to work with Fatal boils down to Balance vs Player Feel. I think the balance detriment will be less than the improvement to player feel, which is why I think it makes sense to allow this to work if that's what the table agrees to.
(saying that though, personally I prefer sticking to the rules and wouldn't use it, but I feel like in majority of cases it's net positive to allow)
Gigantic can't catch a break :(