In response to your statement, it actually is as easy as doubling the ingredients in a 5-gallon recipe to get to 10 gallons. Remembering, of course, a beer recipe is an approximation, a starting point, so the person who had great success on a manual five-gallon rig might not have the same success on a 10-gallon rig. Different processes and tools give different results. Period. So really, the only way you can even use a recipe is to try it and see if you come out with satisfactory results on your system using your processes.
As with everything in brewing, the answer is never so cut and dried. Cheers