I ran the numbers with psp and ds included, and the problem I keep seeing is that the ds, even with a huge drop of 65%,it is still taking up too much of the market. There's only so many people interested in handhelds, and with smartphone competition, there's even less.
3ds MIGHT sell 1.4m in a week if not one person buys a regular ds. Unfortunately, that's not going to happen.
I think Nintendo made a huge mistake in releasing multiple ds variants, ds lite, dsxl, dsi, etc... people are starting to look at the 3ds like it's simply a small upgrade. They could use some more advertising to fix this.