Washout of the wing cord angle is what protects the tip from stalling first. How much has it reduced the tendency? Enough. But remember it as to continue to do so during all the flap configurations. Clever guys.
Wing tips, I believe, are primarily a drag reduction feature. I'm not educated in their design. I would assume they have some affect on tip stall characterises, but what/how/how-much/why is for the boffins to tell me.