(This is meant as a simplified explanation)
Space means a couple of things. Physical space on the satellites is one. You can only put so many channels on a transponder and then you get degraded picture quality. Dish is at that point now perhaps on some transponders.
Then there is the spectrum space. The space allowed for DISH to transmit is defined, just like any other spectrum, OTA or radio, CB, etc.. Adding more satellites can ease the transponder space, but you still have the range of spectrum that is defined.
Then there is setting it up so that the consumer will want the product. Meaning one dish on the house is what the majority of consumers are going to want. Dish has done that with the exception of internationals on 118, by having two arcs, of three satellites each. (118 for internationals needs another dish if you are on the EA)
One way of getting more space is how you process the signal. The Eastern Arc has space because of the newer codecs used that are able to compress better. But there are thousands/millions of people with older equipment that can not get signals with the newer processing so the Western Arc uses the older processing. (Eastern Arc is newer, customers had to get newer equipment to use it) Dish is now starting to make moves to get people to use newer equipment so they can make the Western Arc like the Eastern Arc.
The uplink report actually recently did seem to indicate space was being made, and it would appear it was for the College sports being added, and the new Disney HD.
Finally, Cable absolutely has problems having the "space" to carry channels in HD.