Beach, I understand exactly what you are saying. But.
Personally I think ED made a mistake putting the P-51 in the game without putting the proper environment for the use of the aircraft. Yes it probably made money on the project and that is fine but there was an investment of time and money in that aircraft that probably could have been used to fund a rotary wing aircraft (say, like the AH1-the Huey's cousin) or another jet that would have been much more appropriate in the ED environment. While flying the P-51 is fun in and of its own right most people will want to fly the P-51 in the combat aspect of the aircraft in an environment that would have been appropriate for the timeframe of P-51 production. The Crimea, while an intereating area, was not an area that say much, if any P-51 sorties and certainly not in the 21st century.
You compare DCS to MSFS and there are some valid comparisons but you fail to mention one part. One of the cool aspects of Microsoft Flight Simulator (and later on with X-plane 10) is the ability to fly in different areas of the globe. Probably the biggest sales of FSX and X-plane were to guys wanting to buzz around their hometown in this aircraft or that aircraft. Heck, one of my most fun times in FSX was flying a Stearman out of Galesburg (IL) Airport. YOu also have to remember that almost all of the aircraft created for FSX and X-plane came from third party developers and not from Microsoft or Laminar Research. IN fact, Microsoft washed their hands of the Flight Simulator series after FSX because it wasn't making them enough money.
The other argument is that this is the same approach that 777 is using with ROF. While it is true that 777 sells add on aircraft those aircraft are appropriate to the environment that is Rise of Flight. To me putting a P-51 into the DCS world would be akin to 777 releasing Bf109F4 into the world of Rise of Flight. Great plane, would love to fly it but it would be terribly inappropriate in a WW1 flight simulator. So, what is 777 doing? They are creating a simulation that has appropriate WW2 aircraft.
Personally, if ED is going to do this right, then that is what they are going to have to do. Just dumping a bunch of WW2 aircraft into a modern day Crimea isn't going to cut it. Like 777 they have to create a world where these aircraft can live and fly. Sure ED might sell some aircraft initially, like they did with P-51 when it was released but once people realize the aircraft are pretty much set in a sterile world where they can't effectively do anything then the numbers of aircraft bought will drop. Subsequent aircraft sales will not materialize.
I personally don't think ED is going to just release a bunch of WW2 style aircraft without some kind of environment to play them. It makes poor business sense to do such a thing.