Test position: is it legal to castle?
8/8/8/8/8/7P/1r1n4/R3K2k w Q - 0 1
Think of it this way, you can check a King but you can't check a rook :)
deleted - sry, did not see the first page
Apparently even Korchnoi had to check this rule with the arbiter-1974 Candidates Final v Karpov (his rook was under attack).
Also, maybe check out example given by Jennifer Shahade. White Ra1/Ke1, Black Rb2/Kd8-white to play and win.
May I point to one of my most memorable moves ever?
de.lichess.org/study/oWzjcm1w@Sarg0n Wow, awesome! Thank you for sharing this beauty)
Thx! I remember this one guy spectating and after that move he was staring motionless for a couple of minutes at the board. You could virtually see that he didn't believe his eyes. :D