It's very probable that the PS2 still has the higher amount of sales, but 2.4 million PS2s in stores and warehouses worldwide doesn't sound that impossible. Perhaps it sold a million or so more than what VGChartz is reporting but only somebody with priority issues would freak out about it. DS will outsell the PS2 within a few months anyway.
But you're right about VGChartz not being very credible. It's all guesstimating and there is no transparency in the data whatsoever.