I think that the interpretation of the interview is that 4 to 5 percent of canon buyers buy additional lenses and that the other 95 percent just stick with whatever was in the kit that they bought. The math supports this view.
That's my interpretation as well. Honestly, I would have expected it to be higher, but then it just shows how abnormal (in so, so many ways) forum readers are.
Of course it fits in nicely with my personal theory – which is that one of Canon's strategies for the mature DSLR market is to pivot from selling one DSLR each to lots of people to instead start selling lots of cameras and lenses to fewer people.
Makes sense. With the world's largest installed base of DSLR owners, and in a saturated market where the cost of capturing new customers is growing, they are likely to be focused more and more on up-selling existing customers.
If I'm reading the interview correctly, they believe an inexpensive ultra-wide lens for APS-C buyers is one way to reignite/revive interest among Rebel owners and get them using their cameras in new ways. Pretty clever really.
That's one reason I've been saying the 7DII is likely to be 24 mp or more. Canon doesn't want an APS-C body to compete with the 6D or 5DIII, they want a body that complements their full frame offerings, so we all feel the need to own two bodies – if you want reach and high resolution, you need an APS-C body and if you want low-light performance and low noise you need a full-frame body.
With the right mix, they have the potential to significantly increase their sales of DSLR bodies even if the customer base remains stagnant.