This is made even more complicated by the fact that SpaceX isn't launching from the equator, which means the satellite will need to change its orbital inclination. Inclination changes are less expensive the 'higher' up you are, so SES8 is in an orbit with an apogee almost twice as high as its eventual orbit. This allows it to use less fuel to correct the inclination.
I haven't read up on the burn plans, but it's possible that the mission is technically using a bi-elliptic transfer[1], rather than a straight hohmann transfer (warning: I learned my orbital mechanics from the Kerbal Space Academy).
This alone does not explain why they did so. But this is all assuming that the trajectory is planar. If there was a plane change coupled with the second burn at high apogee, it could explain it.
If there is a plane change involved (as apparently there is), then getting further out before executing the plane change involves less delta-v; performing a plane-change maneuver at apogee is by far the most efficient way.
I haven't read up on the burn plans, but it's possible that the mission is technically using a bi-elliptic transfer[1], rather than a straight hohmann transfer (warning: I learned my orbital mechanics from the Kerbal Space Academy).
[1] http://en.wikipedia.org/wiki/Bi-elliptic_transfer