Sony makes 10 year consoles, meaning, even when a next gen console is released, the last gen console is still alive for the people who don't want to upgrade right away.
ps1's were still HUGELY popular when ps2 came out, because the ps2 came with a 300 dollar price tag
Look at the ps3 launch, ps2's sold more than ps3s the first month of launch, because of it's 600 price tag.
It's all a matter or marketing and pricing that make people want to switch. I'm happy the ps2 is still alive and kicking for the next year or so. Gives people some time. :]