The Cellular has > icon so that we know it has many sub settings. We swipe it to expand the sub settings. We know that the Cellular Data is the main switch of the Cellular feature.
If we swipe it to turn on, the another setting, Enable 4G, appears.
We go back the Settings and find that the Cellular has > icon instead of "Off >".
We enters Cellular again. We know that the Enable 4G depends on Cellular Data. It means that the Enable 4G can be turned on only if Cellular Data is turned on.
If Cellular Data is turned off, the Enable 4G is hidden.
If we turn on Cellular Data, Enable 4G appears again and it is turned off. It seems that iOS 8 remembers the state of Enable 4G.
We can proof the assumption by turning on Enable 4G.
Then we turn off Cellular Data. The Enable 4G is hidden.
Finally we turn on Cellular Data and the Enable 4G displays as be turned on. It makes sense. iOS 8 remembers the state of Enable 4G and shows it only when Cellular Data is turned on.
I consider the GUI is very user-friendly. We can compare it with iOS 7 that Cellular Data and Enable 4G are independent. We are always confused when we turn on/off Cellular Data or Enable 4G in iOS 7, but iOS 8 eliminates our confusion.