I can try it a different way if you like:
1. Start with release of PoP, Oct 2002.
2. Calculate from that time until anticipated release of SS, Sep 2006
3. Number of months elapsed since PoP: 47
4. Number of expansions released since PoP: 8
5. 47 / 8 = 5.875 months per expansion.
6. 12 / 5.875 = 2.04 (and change) expansions per year.
Of course, someone will have an argument why that's just crap too. Whatever.














