In what way are they? I can only see that they are good at chess.

The point is that they didn't come from some "Chess Prodigy" family. There wasn't some "talent" laying there that they picked up. And, even among the sisters, Judit wasn't the one with the most "talent".

Judit's level and achievements were due to training and persistence.

Still they might have a talent for chess and not for ballet for instance. It might be otherwise but that was my claim and the Polgars don't refute it.

Also the Wikipedia page says she was a "chess prodigy". From my personal experience I strongly doubt that you can make every five year old child a chess player who wins blind matches against grown-ups only through hard work.

"Prodigy" simply means you hit your 10,000 hours as a child.

And the "youngest grandmaster" title simply keeps moving downward, so apparently you can convert random 5 year olds into chess experts.

I really don't understand why people still cling to the notion of "talent" in intellectual pursuits. It's pretty clear that "number of hours" is what places you in the top echelons.

When you assume 8 hours a day straight work 10.000 hours means 3.42 years including weekends. I'll claim that's impossible (not to say inhumane) to do with a child.

That's probably a little aggressive, 4 hours a day is more typical.

Go take a look at the history of Magnus Carlsen, Fabiano Caruana, or Hikaru Nakamura.