To be clear, the original purpose of the Spaceway satellites was to provide a satellite based internet service. This is why they used configurable transmission beams (phased arrays) so as to allow bandwidth to be dynamically reallocated as needed. However, the market for satellite broadband never really took off. So, when DirecTV was sold by Hughes the 2 Spaceway satellites were included in the deal. Their existence allowed DirecTV to launch large scale HD service far more quickly and cost effectively than trying to lease space and/or build and launch purpose built satellites (as Dish Network had to do). Their location, very close to the existing satellites at 101, also precluded almost any line of sight issues for existing customers wishing to upgrade to HD and allowed all English language customers to obtain service with a single relatively compact dish (at the time, Dish required 2 dishes for full service coverage).
I submit that it had a whole lot more to do with the fact that the Ku frequencies are mostly taken than it is a proximity issue.It probably also has something to do with the fact that Hughes bailed on a couple of Ka satellites that it had commissioned (Spaceway 1 and Spaceway 2).The reason that they put HD and/or MPEG4 on Ka is because they didn't have a significant number of customers that needed to be upgraded to keep the same service whereas if they had tried to do that with SD, everyone would need new equipment.The need for greater FEC at the more fade prone frequencies substantially negates any benefit of additional transponder bandwidth so HoTat2's argument may be, at least partially, a red herring.
I would hardly say that the increased FEC required for Ka "substantially" negates the benefit of Ka as a transmission medium. Not only are the transponders using wider channels, the higher frequency supports a higher bit rate, all other things being equal. For example, 8PSK encoding puts 3 bits into every radio cycle, so the more cycles per second, the more bits per second. Even with the same transponder band width, using Ka would provide a bit rate advantage, even with the higher FEC.
The main reason wider transponders are an advantage is that the more distinct video channels you can place on a single transponder, the greater the flexibility available to the statistical multiplexers. If we can only fit 4 channels on a transponder, the ability to steal bandwidth from one channel and give it to another (whose data load has spiked momentarily) is reduced versus a situation where I have 6 or 7 channels to borrow from. Ultimately, this allows more total channels to be carried in the same total bandwidth.