Taking your "average ticket prices" data from the National Association of Theatre Owners is a bit disingenuous. I imagine they're averaging over time (rather than per-theatre-attendee or something), which would tend to favor the cheaper, daytime prices. When people go to the movies it's usually after work and on the weekends when ticket prices are $10+. I've seen prices well above $10 everywhere from small town Iowa to downtown Chicago and Minneapolis and they've definitely been higher in the last 5 years.
Add to that the cost of "renting" 3D glasses (a new phenomenon) and the higher ticket price for the "IMAX Experience" (not necessarily new, but much more widespread lately) and your average ticket price is definitely higher than it was historically.
The "average" is the mean of gross revenue ($10.6 billion for 2010) over audience numbers for the year (1.4 billion). This would include both 2D and 3D movies, plus matinee and child ticket prices. It's not clear if they include 3D glasses "rental", but my main assumption is that NATO has always calculated the average this way and they are always truthful with their totals (could be a big assumption).
I agree that a mean loses a lot of information about how ticket prices are distributed. It would be very interesting to see how these numbers trend over time for various percentiles - 5th for cheapo tickets, 50th for median, 95th for high end...
Add to that the cost of "renting" 3D glasses (a new phenomenon) and the higher ticket price for the "IMAX Experience" (not necessarily new, but much more widespread lately) and your average ticket price is definitely higher than it was historically.