Skyheart, having just watched The Almost People (Rebel Flesh 2), and seen the accursed Continued sign, I was reminded that, though each episode usually stands alone, they are doing a great job of running a theme through each season, like Doctor Donna, Bad Wolf and so forth. In fact, I can't think of a 2005 reboot season that Doesn't have some thread through it.
I think it's so that we cope with the few terrible aspects of the show and keep watching.
Examples of terrible aspects:
Plot holes.
Forgotten characters.
Amy Pond.