Seems like that default oversteps the need for editors. It's not adding clarity. It's pimping information for promotion, not genuine interest.
Rather than a default editorial action, why not simply ask the community to put the YC info in the title?
Like I said, it changes the interest for me. I'm less likely to read marketing. I could be in the minority even in this case as a happy Airbnb user.
The YC alums are the editors, that's why some things end up dead and others don't
a blend of advertising and ingratiation
HN is YC marketing, it didn't really start out as an alumni magazine either, but once they realized that they could use it to, you know, sell ...