Disclaimer: I'm not an attorney, etc. etc.

Based on my knowledge of corporate liability issues, it makes perfect sense for the WMF to stay as far away as possible from hosting "real-life" events.  If someone slips and breaks their neck at a Wikimania, the organizing entity could potentially be liable for vast sums of money.  In our case, that's not a big deal; Wikimedia DC will have relatively few assets at that point.  In the WMF's case, on the other hand, they have a great many assets -- and very valuable ones, at that -- that would be at risk in a lawsuit.

Kirill