Ok, the data I have since 2007 is as follows:
Format: Year/New Exclusives / Retirements
2007/ 5 / no data
2008/ 7 / no data
2009/ 6 / 6
2010/ 7 / 6
2011/ 7 / 5
2012 / 8 / 7
2013/ 9/ 3
2014/ 8/ 11
2015/ 9/ 3 confirmed + Red 5. DS, SW, PS, Tumbler???
This is based on EU set launch and retirement dates. I have the full list of launched and retired sets but it is too much work to type up - bbrickset is your friend for that kind of thing.
As we can see, 2013 and 2014 stand out for the few and many retirements but the overall average prior to 2015 is 7 launches and 6 retirements per year (hello Mr Death Star, T1 and Tower Bridge!)