It's easy to answer the OP question:
(A) Split the Wii's attach ratio into two parts -- 1st party and 3rd party attach.
(B) Consider that 3rd party profit on Wii titles is somewhat less than it is on HD titles, when considering raw numbers sold.
(C) Note that Nintendo is always pleased to announce how the Wii has the "most" titles released each year, and then consider that there are negative consequences to that for the 3rd parties, especially given what you've figured out from (A) above, the lower profit margins per unit from (B), and the greater shelf space competition from (C). This raw statistic is great for Nintendo, however, because it means more licensing fees.