Eliminate air losses for defender for anything except "attack air".

[Azaghul]

We've been talking a lot about aircraft and how to re-balance them.  One of the big reasons that aircraft are overpowered is that you can effectively, in one attack, take out several hundred aircraft AND do a lot of damage to the other units of nation (soldiers/tanks/navy).  You can effectively keep someone's air zeroed for free if you're also using air attacks against their other unit buys.  In a blitz, once you have someone's air reduced to ~2/3rds of yours, you can eliminate the rest while attacking their other units with air strikes.

Proposal: Eliminate any aircraft losses for the defender for any type of air attack except "attack planes".  This would make it more costly in MAPS and victory points and resources to keep someone's planes zeroed.