Our area covers primarily two counties; and parts of two others. We also are close to two additional counties that are suburbs of Philadelphia; and two other counties that include areas of the Poconos and "coal country".
I think some of the homes are probably "duplicates" of some of the foreclosures. Banks who have foreclosed will almost always be the ones to show up at the tax sales to pay the taxes before the home goes to tax sale. Government liens (like unpaid taxes) take precedence over mortgage liens. If the banks are overwhelmed with their short sales & foreclosures, some of the tax sales can slip through the cracks until the 11th hour. And some banks might actually lose the properties if they don't catch up in time.
If each of the two counties have 600 tax sales each, then that is the equivalent of 12 to 20 days of "new listings" on our local multi-list service.
A tax sale does not occur until the taxes have not been paid for two years ... hence the reason that these properties being auctioned now are the result of unpaid taxes in 2007.