I believe this is related to follow-on investments from YC after the initial investment
So YC's decisions will impact meaningfully on the ability to raise subsequent rounds.
That probably was true for series B anyway, but now its true at the priced seed round.
I get it - its silly to throw gobs of money at companies that will fold next week, especially if you know they will. But ...
What's changing is the follow-on investments are not automatic. It used to be they would automatically exercise their right to maintain their 7% stake by investing more. Now they're going to maintain a smaller stake, and it's not going to be for every company. Only about 1/3rd of them.