I found something interesting when I was doing last generation PS2-XB-GC comparisons.  When you align the launch numbers, you get this chart:

 http://vgchartz.com/hwcomps.php?cons1=GC&reg1=All&cons2=PS2&reg2=All&cons3=XB&reg3=All&align=1

which shows that the PS2 diverged from the same rate the other consoles were selling at roughly the 39th week mark.  Looking back at the unaligned chart:

http://vgchartz.com/hwcomps.php?cons1=GC&reg1=All&cons2=PS2&reg2=All&cons3=XB&reg3=All

The 39th week mark is still well before the launch of the XB and GC, meaning the decision of the leader was made before the others even came out.  But what happened right around that time that would have caused that decision to be made?  That was around December 3, 2000.  Ok, PS2's first christmas would certainly cause a spike, although it's funny that the spike wasn't nearly as big as the usual christmas spikes.  But from that point on, the slope changes.  Looking back through history, what was it?

According to Wikipedia, there was a supply shortage on the first christmas so only a few million were sold.  It was only after that supply shortage was addressed that the slope changed.  Which suggests that the slope would have been steeper in the beginning had they had adequate supplies and then continued at that rate.  The slopes for the other two consoles remained fairly steady, supply apparently meeting/exceeding demand until near the end of the generation.  Also interesting to note that price cuts for the xbox, gc, and ps2 had absolutely no effect on the slope, certainly not at the point the cut happened.

Current generation chart:

http://vgchartz.com/hwcomps.php?cons1=Wii&reg1=All&cons2=PS3&reg2=All&cons3=X360&reg3=All&align=1

and of course, you see that the Wii is on a much steeper slope and also has demand exceeding supply even at the 30th week mark, which makes you wonder what the final slope will ultimately be when supply catches up with demand.  The 360 and PS3 follow remarkable similar slopes.  In fact, they fit right in with what the original PS2 slope was doing.  

http://vgchartz.com/hwcomps.php?cons1=PS2&reg1=All&cons2=PS3&reg2=All&cons3=X360&reg3=All&align=1

So, for the core gaming market, it appears that the PS3 really isn't out of the race yet.  It is capturing the same size market the PS2 captured, and the 360 is doing the same.  They are both doing just fine.  Maybe not as good as the Wii, but still doing good, which is really saying something considering the price difference from its predecessors.

you are comparing ps2s japan numbers only to xbox and gamecube japan+america numbers.

that is because PS2 was launched first in japan and then a long time later in america.

Ps2 launched in america right at the end of october. So it was only 1 month until the slope you said took place (being it supply constrained from the american launch)

If I had a penny for each time people made this mistake while comparing PS2 to PS3 sales...

Not to mention that the PS2 was sold out while the PS3 has millions of unsold units on store shelves and in warehouses.

The PS2 sold out for the first months in all teritories. It had a WW staggered release date and zero competition. Each time they released in other territories it spiked. MS actually shipped more 360's than the PS2 did in its first year and Sony is trying to match that so of course teh curves are going to similiar. The PS2/PS3/360 curve isn't as similiar as you think though currentl they are both tracking under it. and if you were to allign the US/Japan/euroean launches for each system the PS2 would smoke them all and infact look closer to the Wiis.

But in both cases, the PS3 is way behind.

http://vgchartz.com/hwcomps.php?cons1=PS2&reg1=Japan&cons2=Wii&reg2=Japan&cons3=PS3&reg3=Japan&align=1
http://vgchartz.com/hwcomps.php?cons1=PS2&reg1=America&cons2=Wii&reg2=America&cons3=PS3&reg3=America&align=1

basically, the PS2 had an incredible launch, and the only reason it doesn't look so incredibly is because it was only selling in one region at a time, because Sony couldn't build them fast enough.

Now Sony is building much faster but people are buying much slower. 

This graph says everything. Wii vs PS2 vs PS3 launches in Japan only:

http://vgchartz.com/hwcomps.php?cons1=Wii&reg1=Japan&cons2=PS2&reg2=Japan&cons3=PS3&reg3=Japan&align=1

thanks for posting the exact same graph I posted 10 minutes before you ;) that will really get the poit across.

but ooo, different colours =)

Hmmm... i should PM ioi about this, but I would love to be able to restrict those graphs to only a certain number of weeks, i.e.:

Range: 1-40 

Its a bit too zoomed out at the moment (thanks to the number of weeks the PS2 has been out), to really see what is going on. 

These charts do not include "Europe/Others" data for the PS2 but it does for the Wii, PS3, and 360. So the PS3 and 360 are not even close to the same trend as the PS2. They are both way behind PS2 sales.