Channel 5 originally stated it was going to be 12 episodes I believe. Presumably some of the editing was still going on when it was being broadcast, and a decision was made to either re-edit to fit in less episodes, or some episodes were never made at all.
10 episodes is quite a tall order for just one TOC, especially one that doesn't have those branch lines that allowed Ch 5 to dedicate time to certain events and how people do thinks at quiet, rural, stations.
But perhaps Sky is going to be bigger on the actual members of staff - and follow them more than looking at the actual service and how it's run? You could then, potentially, have them followed even outside of work - what they get up to off shift etc?
I'm guessing here, but I'm very intrigued as to how Sky will pull it off.