That's the problem. Let's say I'm a couple versions behind.. I scroll down to download the latest version, bam spoiled.
Playing devil's advocate, let's say you've never played and see the title, the images, etc. & expect to get Grandma in bed.
Then you'd probably be disappointed & come here to complain that you can't fuck her yet.
So the OP's disclaimer aims to prevent that by informing people.
Being told you cannot fuck a primary character (yet) is not a spoiler. Lots of games have extensive build up to the main event, with a main LI. It really shouldn't be a surprise.
Hence, being told that you cannot fuck her doesn't spoil anything. It merely allows people to manage their expectations.
Being told when you
can fuck her is more of a spoiler, IMO. So called because it literally spoils the pleasant surprise of the main event's arrival.
If you're referring to the removal of that disclaimer being the spoiler then, as
Wolfeszorn said, it's a bit of running gag by now, so may well remain there long after the game is finished. I'd certainly expect it to still be there for a few versions after she's hopped on MC's junk, so don't worry too much.