I just don't see that kind of run. The idea of an 8 year run seems to be based on the idea of the systems power. The notion that it's so powerfull that it will continue to push the graphics envelope for some time. But power isn't what keeps a console going, games is. Look at the current/last gen. The xbox was by far the most powerful system, but the PS2 had the market share and the games, which has kept it going along at a steady clip even today. For the PS3 to do those kind of numbers, it would have to keep the third party dev's interested in it specifically. But with the improved 360 sales and the Wiisplosion(I'm trademarking that), it seems unlikely.
Edit: "7.5m units sold (PS4 announced, or agreement with MS on a join project)" - Wha!?
The PS2 is thus far has been out for 7 years as of March 4 2000, October 26, 2000 and November 24 in Europe. The PS2 didn't have fancy-dancy stuff in it as opposed to what the GC did or Xbox did. However, it had a dual core processor that even though was dumb (ala Saturn, ala PS3), it atleast future-proofed the system between that and the DVD to allow for alot of improvement.
The secret to the PS2 doing 115m+ units shipped belongs to 2 reasons:
1. Strong Library (best library in the history of gaming, encompasing every genre, multi-platform game, and far too many exclusives)
2. Developer Commitment/Support from Sony and other developers (there are still titles coming out for the PS2 even into the PS3 lifespan)
Those 2 reasons allowed it to exist for 7 years, and might see sales the rest of the year. The Xbox fell off the charts immediately when MS decided to ax the program. The GC has still sold (not much, but still sold) in the US because Nintendo released games like Zelda: TP for it, with other scraps. When a company decides to support a product for quite some time, eventually something will give.
Developers will continue to support the PS3 as a multi-platform system like the Xbox was, and 360 is. However, Sony still has a few ever-dwindling major franchises that provide a worldwide advantage. Not only this, again, since the system is "future-proofed" (tm), 4 years from now developers will still use it as a multi-platform system to still create games on when Nintendo and MS are preparing to switch, which is why I believe it'll do well late into it's cycle.
NO ONE would of thought that 7 years ago, the PS3 would beat out each and every next-gen system in the US in December and still sell nearly 6m units in the US alone. I am just stating the same will happen 7 years from now - just not with as much razzle-dazzle as the PS2 did in its early life.
Again, look at what Sony did with the PS3:
Large HD support for downloadable games and virtual content (imo, something this gen will have alot of)
Cell prcoessor (right now, a piece of junk, and every dev has said they can't use it properly. However, it's still 6 cores @ 3.2ghz. It might take 4-5 years for devs to even make the cell more powerful than the X360's CPU, but it'll happen. Allowing the PS3 to overtake the 360 in terms of the graphics race)
HDMI (HD stuff that I don't care about, but still, future-proofing)
Blu-Ray (yes, slow, but large capacity. Not that important and costly, but 4-5 years from now, devs will find reason for this kind of space).
Again, we see the 360 and PS3, and the 360 is whomping it graphically due to the same reasons the PS2's graphics weren't good: documentation software wasn't great, the dual-core PS2 was difficult to pull alot of power out for. However, they kept working with it till it worked great. Thats why we have Guitar Hero 2 and God of War doing great. They are still good and current enough to keep up with stuff on a 7 YEAR OLD system.
I'm not saying devs will goto the PS3 as a lead console. However, in 4-5 years when devs prepare to switch to the Xbox 720 and Wii 2, the PS3 will still be there with enough power to possibly hold some water to both systems visually. This will allow devs to multi-plat for the 720, Wii 2 and then the PS3. Add in the past 4 years of software and a price under the Wii 2 and 720, and you have something that continues to sell well.
The PS2 still has another year in it, and could sell another 10m units and wind up with 125m units. Really, the PS2 didn't out-do the PS1 much (about a 15% increase over a longer timeframe). But what it DID do is break the 6 year barrier every system has had (dying out in 6 years. Most systems loose any support that late, the PS2 hasn't).