I feel you man, but I am pretty sure we will get the new map on Steam soon enough. It is frustrating though to have purchased modules for DCS on Steam only to find out that the Steam version gets different treatment from ED. Wish I would have known this before hand, and I know others feel the same way.
I am pretty certain that Steam would allow ED to put the Persian Gulf map and F/A 18 up for pre-order as well, but for some reason, it seems that the release dates and pre-ordering are exclusive to the standalone version.
The only excuse I have heard is that they fear negative reviews on Steam. Doesn't really make sense though as the discussions over on Steam are pretty much "Hey, where is the map? I was looking forward to buying that". Also, treating the Steam version like this only makes people who bought modules from Steam feel like they have missed out, and I am constantly seeing threads of people asking if they can transfer their modules from Steam to standalone.
I really hope they get this is order so that us Steam users don't feel so left out.