, one issue is that you don't get a lot of vertical diversity in triangulation using ground-based objects, so your vertical angles are pretty acute. Also, most location techniques that use wifi just match signal strengths against a pre-sampled location map, gathered by a vehicle driving down the street, so there's no vertical knowledge in that map. There's no way to "triangulate" against a wifi AP as the timing is just too sloppy and signal strength is not a usable indicator of range. Also, nobody knows exactly where the access points are, including the APs themselves.
(If it's not obvious, I spent way too much of my life trying to get a non-GPS geolocation system working.)
The baro chips typically include a thermometer, so they can at least compensate for temperature effects, if not pressure fronts. They're certainly close enough for many uses, especially for relative measurements.
Besides, most of the time, the best guess is just "ground level" from a topo map. :)