400,000 more Facebook users list Philadelphia as their location today than in 2010

Some 400,000 more Facebook users listed Philadelphia as their location earlier this month than did in January 2010, according to much trafficked data from iStrategy Labs that circulated it way across the web.
As can be seen in the chart above, Philadelphia had a middling rate of growth during that time period — 32.4 percent — in comparison with other big cities. There is no clear mention of expected margin of error, considering these are self-reported location statistics.
It’s interesting to note the dramatic plunge for all listed cities in their overall percentage hold of U.S. Facebook users from last year to now, due to continually fast growing user-ship. It’s not just all youse damn urban elites.
Get more perspective from iStrategy and from AllFacebook, which, perhaps dubiously, claims these figures suggest 71 percent of all Americans have Facebook accounts. We wonder how many fraudulent accounts are included, considering we at TP have more than a few Friend requests sitting in our queue from friends’ pets.
What else do you think is wrong with these numbers? Or are the potential flaws just more apparent but no more damaging than in other collections?