The Army fly's both. The ISR mission is known as TF ODIN and we have been doing it for some time.We started it in Iraq. We also fly the RC-12 which is the Guard Rail mission. Two totally different missions.
Seems like the Air Force wasn't really interested till the Army started doing it and was in line to get more airplanes. Same applies to the C-27.
I know all about Task Force Odin's good work and know full well the differences between the RC-12 and MC-12, but there is still very good reason for the Air Force to take over the 'Liberty' mission. Both the USAF and Navy have a surplus of aviators right now, many of whom have quite a bit of experience with ISR. The Army's experience in ISR is not as broad or as deep as either the Air Force or the Navy and would probably have had considerable difficulty absorbing the large numbers of MC-12's entering theater right now. Why? The Army has long not had it's airborne ISR as one of it's higher priorities and it showed. I think one big reason is that much of the expertise in this arena is at the CWO level and they aren't able to best represent the communities at the level it often matters for the communities and their long term health, field grade and above (program management, joint staff and COCOM representation, etc). Most of the Army O-5 and O-6 aviators from the ISR arena I have met didn't have the same breadth and depth of knowledge about their mission areas as their USAF and Navy counterparts, not through any fault of their own. And those guys are very few and far between, leaving a gaping leadership hole at the higher levels. I think the Army's train wreck called Aerial Common Sensor was a direct result of this.
Why does that all matter? The Army had almost it's entire part of it's manned ISR knowledge residing in 4 battalions of aircraft that are already stretched thin. Their expertise in ISR was also very specific, focusing largely on one particular segment of one 'INT'. The Army's lack of knowledges when it came to the larger ISR/electronic warfare arena became painfully evident when the Navy had to plug its EW hole with hundreds of personnel starting in 2006 and continuing today so it is not like the Air Force is doing something much different, they are just running the show in this case. And doubling the Army's manned ISR force almost overnight would have been unwise to say the least, especially when they have hardly any 'back-end' aircrew to speak of. The Air Force might have swooped in and grabbed it but they were probably right to do so, with the infrastructure, institutional knowledge and personnel to get the job done, along with a big assist from the Navy.
It is less about service parochialism than it is simply getting the job done and the Air Force jumping in with both feet, prodded explicitly and repeatedly by the SECDEF himself, was likely the right thing to happen.