I think the number was always 6 mil by March, 4 mil by end of '06, and 2 mil at launch. They missed on the 2 mil, and 4 mil milestones already, yet they are still insisting on the 6 mil number. Which is kinda ridiculous, I doubt they'll sell half of that.
It looks like they are trying to ship 6 mil so they can claim they are just as successful as the Wii... even if PS3 starts to pile up in warehouses around the world. At some point, retailers are going to run out of shelf spaces, as those boxes aren't exactly small, and start begging Sony to stop shipping the thing.