Small coincidence of Showrunners

I have long notice a coincidence between the showrunners of New Doctor Who.

There are two coincidences that I have noted. 

1. Minisodes

During Russel T Davies' era the only other writer to write a minisode was Steven Moffat who wrote "Time Crash". Obviously Moffat succeeded him. During Moffat's tenure as showrunner the only writer to write a minisode that wasn't him was Chris Chinball who wrote "Pond Life" and "PS". Now Chinball will be the new showrunner

2. Two-Parters

In both Russel's and Steven's first series of Doctor Who they wrote 2 of the 3 two parters. The other writer for Russel's first series was Steven Moffat who succeeded him and in Moffat's first series as showrunner the other writer was Chinball who is going to succeed him.