This has sparked much choice comment on the blogs and fora but but the decision is justified in a well thought out developer blog entry.
There is some technical justification for the block but it seems it is mainly a deliberate design choice. The blog cites role play reasons: the block is required to fit in with the game lore. Also and perhaps more significantly they don't want this new form of pvp endgame to pollute the hard core alliance war end game and nor do they want the hard core alliance end game to pollute this new game.
It sounds to me as if CCP want zero-zero alliance warfare to remain the pvp endgame for hardcore players and are introducing faction war as an alternative for the less dedicated.
Interesting times. I wonder if they will get away with it. Can you imagine if Blizzard introduced a new endgame dungeon into WOW but excluded any one who is in an established raiding guild from entering it?