Why would their availability for war be any different? You choose to upgrade them - they aren't available for regular attacking/protecting during that 7 day upgrade, so why would they be available for attacking during war?
We already get the added benefit that they are available to defend our base during war, as we do with the defensive structures.
Despite the name of the game being Clash of Clans, Clan Wars is only a small portion of the game. Multi-player attack mode still drives the game - look at the number of top players that have very few war stars in their achievements.

