According to this data, after the PS2 came out, the PS1 sold about (shipped):
4.19 mil in Japan (19.4% of total)
12.13mil in NA (29.7% of total)
10.78mil in EU (26.9% of total)
That's 27.1mil worldwide, or ~26% of its total 102.5mil shipped. The argument that the Wii will die because the next Nintendo console will destroy it is put into question here, as even with its massive success and backwards compatibility the PS2 did almost nothing to stop the PS1 from selling.
Some conventional wisdom put into question from this: The PS3 selling poorly or being too costly is not making the PS2 sell better! The PS1 may have relatively better post-gen sales than the PS2! When the PS3 came out, the PS2 already shipped 24mil in Japan, 44.9mil in NA, and 44.8mil in EU, so 113.7mil total. To match the PS1's post-gen ratio, it'll need to end up shipping a total of 154.5mil PS2s. I don't see that happening.
