For now. If their service gets enough uptake, though, it's not hard to imagine other publishers wanting to get in on it as well. And why build your own service (and go through all the hassle of getting it on all the devices in the world) if you can just piggyback on EA's work? (As long as the fees and contracts are reasonable, of course.)

When Steam started out it was only a delivery channel for Valve titles, remember...