The pie charts seem like an odd way of counting some of these; for example, one site could use Facebook Like, Google +1 and a Tweet button all at once, but showing them as slices in a pie chart implies to me that the options are mutually exclusive.
The pie charts also don't match the percentages in the tables. Took me a second to notice, but the pie chart shows the relative percentage of usage by sites using a particular category, while the table shows % sties out of total # of sites.
Not just odd, but completely wrong. For data that doesn't add up to 100%, they should be using a bar chart or some other representation of data. Unfortunately, this is the sort of sloppiness that makes me wonder what other amateur mistakes might have been made in collating the data.