Those are very interesting numbers. Two observations:
The “65+” category is unbounded on its upper end. As a general rule, more people are staying healthier longer (or at least healthy enough to work). So, if one was to look at, say, persons 75 years old (only), it would stand to reason that their participation rate has increased — even if they are just the greeter at Wal-Mart. That would push up the participation rate for the 65+ age group.
Anecdotal evidence would seem to suggest that when it comes to persons in the 55-64 year group, many primary wage earners have lost jobs, and either have not found new work, have only found work at a lower wage, or have retired. However, their spouses are either continuing to work when they otherwise might have retired, or, in some cases the spouse has entered the workforce to give the family a second income to try to bring the total back up to what it previously was. Are there any statistics that might support or disprove this idea?
IMO most Americans have not saved for their retirement. They will have to work to survive. About one-third of Americans over 65 depend on SS as their sole source of income.