Seems to be a bit misleading. They are basing their numbers on averages not actual salaries. If Obama has more male than female staff members then the numbers will be skewed. Look at actual jobs and salaries. I found this
site that lists the jobs titles and salaries. Hard to make sens of it when they do not tell if the jobs with the same descriptions such as
Constituent Services Agent are in the same area and have the same level of responsibility or not. That may account for the pay difference. Legislative Assistant seemed to be all paid the same regardless of gender.
There is also
this article (which references the above site where the numbers were supposedly found). Unfortunately the article does not mention actual names so it is hard to verify the data. I think the premise is accurate though. If the jobs are the same the pay should be the same. Averages of entire staffs do nothing to address the pay equality issue.