Comparing Wii to PS2, it seems right in line, (with the exception of PS2's odd jump in 6th year, however, that is inline with its 7th year and same rate of decline). However, that jump in its 7th year may allow PS2 to remain higher in the long run.
7th year I expect about 8M, so about 100M towards endof 2012 sounds about right.
Buying in 2015: Captain toad: treasure tracker,
yoshi woolly world
majora's mask 3d