Rook immune to Capture?

This has most likely already been discussed, but can anyone help me understand a situation from a classic game (Steinitz v. Von Bardeleben). During the game the black King is checked by a Rook (Rook that Castled earlier) around move 23 of the game. I've read that it is some form of etiquette that this particular rook was immune to capture. I am pretty sure that by capturing this rook, black would have been mated in 3 moves anyway, but just hadn't heard of an immune rook before. Does anyone know why or when this originated?

Can you show us the game?
 

Immune from capture because black is mated if he captures the piece. Etiquette has nothing to do with it.

It's still not immune to capture. You can legally capture it but will get checkmeted as a result.

Well, yeah, but that's what's meant by the term in chess. It's not literally immune...

Here one second and I'll show you, but he is not immediately mated if he captures it. 

http://www.chesshistory.com/winter/extra/steinitzvonbardeleben.html

1895 Hastings tournament Steinitz v Von Bardeleben. Sorry couldn't post the move by move, but he could have taken the rook with his queen easily...

If he takes the rook with his queen white has 26. Rxc8+ Rxc8 27. Qxc8+ and white is up a knight. That's if there's nothing better.

Great article on the game, but I am still at a loss as to why he wasnt able to take the rook with his queen?

As above, he's a knight down and easily losing.

Move 22?

The same pattern.

Thanks Scottrf and neo-metacrash, by the way where did you find that cool game analysis link?

Nvm i see it. Thanks

White is winning here.

Post #11's statement that Black resigned and Steinitz immediately demonstrated the win, I believe to be incorrect.

I'm pretty sure this is the game that Von Bardeleben left the tournament hall (in a state of considerable agitation), clock still running, once he'd figured out his demise. After VB's time expired, Steinitz demonstrated the win, for the crowd.