It's also why (among other reasons) the UK peerage doesn't have "Counts." It uses the old Anglo-Saxon "Earl" for county-level peers even though the Norman system largely displaced the Anglo-Saxon system after the conquest. Curiously though, the wives of earls are countesses.
The jarls still held a lot of land, especially in the north, even after the southern kingdoms changed hands. Medieval feudalism was never a simple one-party dictatorship. Balance of local power probably has more to do with the propagation of nomenclature than simply having a new guy in a castle several days' journey away from your village.
