Seeing as it's not the answer and I have NFI but want to sound smart and stuff, another interesting thing about that series is that England won every game by 6 wickets.
Well, from a team perspective, a team winning every game in the series by the same margin is unique. However, in bilateral ODI series (2-8 matches), this also occurred in
- 1983, India beat Pakistan 2-0 by 4 wickest in both games.
- 1998, Pakistan beat Zimbabwe 2-0 by 4 wickets in both games
- 2003, England beat Bangladesh 3-0 by 7 wickets in all games
- 2007, Kenya beat Canada 2-0 by 4 wickets in both games.
However, I'll give you credit. Good observation and another clue, you are on the right track!