Bob, very interesting. Now, you'll have to forgive me, but I want to twist your numbers to suit my pet theory.
My Theory- I'm convinced that HCH 2 owners are more committed to getting "great" FE than Prius owners.I'm also convinced that it is easier for an average criver to get outstanding FE with a Prius 2 than with a HCH 2.NOW I'M NOT SAYING THEY ARE CHEATING-NO WAY-I'M JUST SAYING THAT A HCH 2 OWNER ON THIS FORUM IS MORE LIKELY TO DRIVE TO MAX HIS/HER FE. It is a probably point of honor for FE fanatics to be scrupulous in respect to honesty.
How can I prove this?
Well,I can willfully over interpret your numbers and "say" that the fact that more than 50% of HCH 2 get better than average FE means that the HCH 2 data has more "committed" drivers-committed being defined as "better than average."
The Prius has exactly as many above and below average drivers-median and mean are the same.
Of course, the numbers are so close, they really don't support my claim very strongly.
My strongest evidence comes from the much hated CR numbers.CR drivers did much better with the Prius 2(city 35 hy 50 trip)48 than the HCH2 (26 47 45). CR doesn't use any FE tricks; many members of this forum do use FE tricks, and I think HCH2 owners use them more than Prius owners.

On the subject of Toyota tuning the Prius to produce "Great" EPA FE. FE that -in respect to city mpg- is far, far removed from real life. OF COURSE TOYOTA DOES THAT-WHAT COMPANY WOULDN'T? Now does this mean they have to give up some "real world" FE to achieve their "fake" numbers?Of course not; that is the beauty of having fairly complicated ECU with lots of memory,and having EFI with O2 and air mass sensors that give many,many readings/second. You can set it up to give great "fake" numbers while not giving up anything real world. We aren't dealing with a carb that can give good FE at one throttle opening/load/altitude, but has to give up FE/power everywhere else to achieve it.
I'm biased, but I'm also convinced that your numbers indicate that the HCH 2 data indicates that more of them are FE fanatics than Prius owners.It is easier for an uncommitted driver to get good numbers with a Prius 2 than a HCH 2. Thanks,Charlie
PS If I was even more biased,and had even less of a life, I would check the total number of posts by HCH 2 data providers-get the average, and compare it to the average numbers of posts by Prius 2 data providers.
If the numbers showed that HCH 2 data providers post more than Prius 2 data providers, I would immediately claim that AVERAGE NUMBER OF POSTS IS A PERFECT MARKER FOR FE FANATICISM,and claim my theory as proven.If the numbers don't show that-then I wouldn't report it,since I'm a typical biased cheater!!Just kidding about the last part.