Obviously, no test cycle will perfectly duplicate all real-world conditions, but in general the North American (EPA) test cycles are generally considered more likely to reflect real-world driving scenarios than the test cycles used in Europe (NEDC) and Japan, which tend to have more unrealistic assumptions about how people drive in reality. (Incidentally, while the average or mean speed in the U.S. high speed test is 48 mph, about half the test is continuously between 60-80 mph with some "stop and go" at the beginning and end.)
For example, your F-150 would probably actually get a higher highway mpg rating on NEDC, if Ford sold it in Europe (which it doesn't), which would be even less realistic than the 10% drop-off observed from EPA at 60 mph and 30% drop-off at 75-80 mph.
My assumption on why the Clarity seemingly outperforms the EPA ratings is that most drivers have some experience with EVs or hybrids, and so are consciously or subconsciously using "hypermiling" strategies to some extent rather than the aggressive speed changes that are tested (look at the graph for the city cycle at the link). The Clarity is also tested in its "default" mode, which is not ECON or HV; the 42-44 mpg figure derived from testing is probably accompanied by the angry bees, since the gas tests are done starting with a completely depleted charge and you're not going to get much regen to smooth things out.