@graykevinb has it correct: the new operating system DexterOS creates a pairing WiFi hotspot for an easy connection. The wifi dongle works better than the Pi3 wifi for this. So we ship it with the Beginner starter kit.
DexterOS also works with the onboard Pi wifi, so if you want to order it ala carte, you're welcome to take the dongle out! Be forewarned you may not have as solid of a connection with the Pi3 built in wifi though.