I can't really speak to the Romney campaign's use of salesforce, but I never had to deal with it as I believe that our use was limited to handling inbound contacts from public channels.
The Obama campaign had the distinct advantage of having 18 months to build our technology from the ground up, and that's precisely what we did! Of course, there were still external vendors that handled some functionality and we built systems so that everything was integrated and worked together.
Typically, a Presidential campaign only has 3-4 months between when they secure the nomination and the election to build their campaigns, which is why there are many niche vendors. Romney undoubtedly got an influx of support from the RNC once he had the nomination, but they could have easily have continued building since he never collapsed his organization from his 2008 campaign.
The big difference in my opinion was the choice to bring a dedicated internal term in as opposed to outsourcing to consultants.