I don't think the theory is entirely without merit, but your anecdotal observations don't gel with mine.
I don't notice any difference between education level / age on PS3/360 in broad strokes. But at least in people I know, with one exception everyone who owns a PS3 also owns a 360. But lots of people own 360 and no PS3. The one exception was a guy who had no university degree (and potentially no high school diploma), as he was a mover who was moving me a couple weeks ago -- he only had a PS3.
In my observations and experiences, the PS3 is purchased after a 360 as an auxiliary game console/bluray player. People treat it as more of a luxury item, to enable them to play all games, like I do. The 360 remains their core gaming machine, while the PS3 is a "nice to have" extra.
This, too, would explain why PS3 sales suffer and 360 sales remain strong. The 360 is, for all practical purposes, most people's primary gaming console while the PS3 is a secondary console. At least this is the case with people I know here in Canada, with a heavy bias towards 20-40 year old technology professionals and their friends.
I originally would have agreed with this, however...
The problem arises in that 3rd party titles that are cross platform tend to sell quite well. At least the popular ones. The less popular ones tend to sell significantly better on X360 it appears. Skate 3 for example.
But anyway, back to the point. Popular 3rd party titles tend to sell (in NA) fairly close to the X360/PS3 install base division. GTA4, CoD4, CoD5, etc... There are some exections however, SF4 doing better relatively on PS3.
While 1st party titles generally tend to do quite a bit worse.
If your theory was true it should be quite the opposite of that since PS3 exclusives aren't available on X360 then people that have a PS3 also would be more inclined to buy those for PS3 rather than say GTA4 (which they can get on X360).
But that isn't happening. Big budget exclusives for the most part are seriously lagging behind big budget cross platformers on PS3.
However, the fact that sales of big budget cross platformers tend to die quite fast on PS3 compared to X360 might be explained by the theory that many X360 owners also have PS3's.
The sales numbers I'm most interested in seeing going forward are...
1. God of War III being a runaway blockbuster. I very much expect it will be, but then PS3 owners have surprised me quite often in the past by not buying as many games as I expect them to. If it isn't a runaway blockbuster, I just don't know what to think of PS3 owners.
2. Halo: ODST. By all accounts, even with the Halo name it shouldn't be a runaway blockbuster. It's a "budget" FPS title. It's being released into a market supposedly "flooded" by quality FPS titles (one reason put forth by others that KZ2 didn't sell to expectations). So, while it will probably chart it shouldn't have phenomenal sales, but I have a feeling it's still going to sell like gangbusters. Moreover, I have a feeling that many of the sales won't be driven purely by the Halo name, but by word of mouth.
3. If Final Fantasy XIII releases simultaneously on PS3/X360 in NA, how will it do comparatively on both platforms. I "think" it should do better on PS3 than X360, but I wouldn't be surprised if it followed install base splits or did better on X360.
Regards,
SB