You can have up to 4 orbitals, they can be from eastern or western arc, which requires a dpp44 switch, and no, the channels themselves are not different depending on what orbital you pull them from.
What orbitals you receive depends on your locals most of the time. Or if you have no line of sight for your normal orbitals, the opposite arc is usually used, however in this scenario you usually lose local channels. Unless they are able to wing in your orbital for locals.
Most international channels come on 118.7 orbital, so they receive the western arc with a wing dish pointed at 77 if their locals come off eastern arc.
Only mpeg4 receivers can decode the signal from the eastern arc, meaning HD receivers. This does not make SD channels look better though.
Western arc has much higher signal strengths than eastern arc, but I couldn't tell you if that actually causes more signal loss or not. Or if eastern arc has higher signals in other parts of the states.
For instance, in Baton Rouge we use western arc. SD locals are on 110, HD locals on 129. If the customer has no line of sight for western arc, we put eastern arc if they have HD equipment, and wing in either 110 or 129 if possible. However just 2 hours west in Lake Charles, their locals are on 77, so they usuallyuse eastern arc.
