Yeah, mine's £85 for the 3 (WSU) so I'm not going to complain about £28 per game. Plus its an early OPTION, you don't have to take it up. As you say, the clubs played this right.
I would assume, like any other Cup game, that STHs will have a window to secure their own seat for each individual game before it goes on general sale.
There's no reason whatsoever to expect STHs to cough up for all 3 games in advance.