The figures for sales for the last year of 998 production and first year of 999 production were quoted by Ducati themselves in MCN and they were very happy with the 999 outselling it's predecessor.
I think the main reason for falling sales is the Japanese competition is getting much better , older blades and GSXR / ZXR 750's were similar performance to a 916 / 96 / 98 at a cheaper price , todays R1 / GSXR1000 / ZX10R are way ahead on power compared to a 999 and still a lot cheaper.
WSB is also no longer a big seller for bikes , as much as I thought (and still do) that Foggy is a complete pratt his success sold an awful lot of Ducatis , I think Rossi's popularity and TV coverage of MotoGP is doing for Honda and Yamaha now what WSB did for Ducati 10 years ago.
.......now , if we could just get Vale to ride a Desmosedici , then watch 'em fly out of the showrooms