lat,lon doesn't have any precision attached to it. Also, you might be surprised how many times people get them reversed. Hey, even geojson encodes it as lon,lat.
Also easily normalizing (lat,lon)s isn't so straight forward.
And then there's subtleties when people are actually not using the WGS84 but a crs/datum one shifted a few tens of miles.
Sort of surprised that nobody compares this to geohash[0], though.
I hope that Google will be throwing its weight behind it (seems so for now) and proposes a rfc for this so we can stop bikeshedding about geo encoding standards.