I think there might indeed be more people who own a PS3 than people who own a 360.
The number of shipped console is always higher than the number of people who own a console, one reason being that some people own more than one console.
From my experience, the percentage of people who own more than one 360 is a lot higher than the number of people who more than one PS3. One major reason is the fact that the 360 can so easily be modified to play pirated games and that Microsoft bans modded consoles at least once a year. Every single 360 owner I know owns a modded one. Obviously that is not representative for all 360 owners, but I'm sure the percentage of people who own a modded 360 is quite significant, just like the number of owners of modded PSPs.
Since Microsoft bans modded consoles at least once a year, these people usually own at least two 360s. One that got banned and which is used to play pirated games offline, and one unmodded 360 which is used for playing original games that the person really wants to play online. If a modded console gets broken - which is almost guaranteed to happen sooner or later if it's not one of the newer revisions - then these consoles are not returned to Microsoft for repair because they refuse to repair it or they would charge a ridiculous amount of money. So they buy another 360, mod it, and the old one usually goes in the trash or some cupboard. There is a 360 internet forum that I visit from time to time where I have seen lots of people saying that meanwhile they have 4 or more 360s at home.
And even many owners of unmodded consoles buy more than one. As everyone knows, the failure rate of the 360 was ridiculously high for most of the 360's lifespan, and at some point even 3 years of warranty against RROD were over. Repairing those units doesn't make sense, those people will instead simply buy a new one.
So I think there might indeed be more owners of PS3s. But in the end - what does does that mean anyway? I think for the manufacturers other numbers are much more important than the number of owners.
