Keep in mind that Wikimedia is managing a lot of community volunteers as well as their direct employees. The travel expenses may include paying for some of their volunteers to visit them, for instance.
It's also worth noting the foundation has had issues to expense irregularities in the past [1], and so if anything there is cause to have pessimistic assumptions rather than optimistic ones
[1] http://www.theregister.co.uk/2008/03/05/jimmy_wales_and_dann...