I think the real reasion the US do not use the Longbow radar on their apaches in afganistan (i know you said iraq) is because of the heat. Do to the hot air it makes it harder to take off with a heavy payload. Therfor they can take of with more weapons without the heavy radar so they choose the weapons.
The UK doesnt have this problem because they customised their apaches with a more powerfull engine (and fold away roters so they can use them on ships. oh and a much better self defence system) therefor the UK apaches (Apache AH Mk 1) carriers the longbow radar in afganistan and the full weapons suit.
It is said the US is thinking of buying the UK's engine and selfdefence system + adding a better gear system so they to can use the longbow in afganistan.