This is because the the esp 8266 boot ROM runs at 74880 Baud.
Many people complain at the 'choice' of 74880; well there is a technical reason for it.
From here https://groups.google.com/forum/#!msg/esp-open-rtos/_j7MffxhqsA/XVfzemznBQAJ (See the post from Angus Gratton at top of page)
I found this explanation
On reset, ESP8266 hardware default baud rate depends on the crystal choice. With a 40MHz crystal you get 115200bps. With a 26MHz crystal you get proportionally less, 74880bps (115200*26/40). Almost everyone (including Espressif) ships hardware with a 26MHz crystal, so almost everyone gets 74880bps by default.
One problem is that some terminals do not support the 74880 Baud rate. To overcome this I use Coolterm. For details see this post http://www.esp8266.com/viewtopic.php?f=32&t=2664&hilit=+coolterm
Hope this helps.