I think your figures are in line with my own experience, but remember that individual driving patterns have a *big* impact on the mileage, and that may explain a lot of the variation seen in the mileage database.

For example, I can reliably achieve 45mpg on 30+ mile suburban trips (avg. speed 40mph), and 35-37mpg on long highway trips (avg. speed 70mph) - but my daily commute is about 6 miles each way (not enough to warm up the engine the whole way, in winter) and I only get 37-38mpg (32-33 in winter) on that route. So if my commute makes up the majority of my driving on any particular database entry, my mileage usually suffers (especially in winter).

For reference, my last car (with a 2.5L V6) averaged 22mpg under the same driving patterns. By comparison, 32-38mpg looks really good.