Ah, so you don't have the plane yet right?

For the most part, most "entry level" electrics that use 2S or 3S LiPos, NiMH or NiCD packs use an ESC ( Electronic Motor Speed Controller ) with an on board BEC ( Battery Eliminator Circuit ).

The BEC grabs some of the current provided by the battery and steps it down in voltage for the servos.

On bigger electrics, e.g. those that use 4S LiPo's and above, it is customary ( but not exclusive ) to see separate BEC's used to circumvent the need for a servo/receiver battery pack.

A BEC is MUCH lighter than a battery pack and separate BECs can be purchased for 9.00 or so, though the owner must wire them up.

The plane you posted the link to, normally has it's RX and servos powered off the BEC on the ESC you purchase for it.

To confuse the issue, most on board ANALOG BECS ( there are also "switching" BEC's as well ) can only provide power to 2-3 servos when using LiPo 3S cells or 10v+ NiCD/NiMH. The reason for this is the HIGHER the voltage the more energy must be dissapated as heat to lower the voltage. Switching mode BECs use a different technique, but are not always provided on ESC's and only very rarely on high voltage/high power ESC's.