That is why oil change is such a hotly debated topic.
A lot of people feel exactly as you do. They will only use what is specified in the owners manual. I understand your position.
The owners manual has more than one print version. Some owners manuals say that Ford recommends Castrol. I have a Ford truck with a fuel cap which says to use BP Fuel. I wouldn't get very far, because there are no BP Fuel Stations in my area. I have heard that it is simply a business decision to print a recommended brand into the owners manual. The cars are not specifically engineered to used one specific brand of oil. Others will also point out that as per the owners manual, you will be fine as long as you are using oil with the API starburst logo.
My personal choice is to use the correct weight oil, and change oil at or before the recommended maintenance schedule, or follow the recommended maintenance schedule for severe duty.. My driving is at low speeds, stop & go traffic, and extended idle sitting in traffic all day. Yet I see how plenty of people will post their used oil analysis report to prove that they can drive for 10,000 miles or more with their choice of oil brand. I don't think that you have to use Motorcraft only. I have no problem with using Motorcraft, and use it every chance I can get a good price. Just picked up a case of Motorcraft transmission fluid, since it was even less in cost than the Wal*Mart SuperTech brand. While Motorcraft brand oil & filters are good, there are other options.