...I expect the PS3 to end up close enough to the PS2, probably somewhere inbetween the PS1 and PS2.
Seriously?
The biggest difference between ps1&2 vs 3 is ... well ermm ... there are too many to list just one!
price
competition
software library
launch timing
hype/marketing
I'm sure there are more I can't think of at the moment.
PS1 and 2 both were in very different ecosystems and were very different product offerings.
Price-
PS1 $300 ... followed by price cut to $200 (that's where that big sales spike came from btw)
PS2 $300 ... followed by price cut to $200 (that's where that big sales spike came from again, btw)
PS3 $500-600 ... I don't know when they will get to $200 ... but I imagine it may take them a bit longer to reach than PS1&2
Competition-
PS1 vs Saturn (N was late to the party with a so so product)
PS2 vs DC (N and MS were late to the party)
PS3 vs Wii & xb360 (Sony was late to the party ... err wait that comes later)
Games-
PS1 - They had every dev and publisher under the sun working on a technically impressive console that was easy to dev for to boot! Exclusivity on a few heavy hitters helped their cause as well, but the overwhelming support from every major and minor player in the games world is what established the PS brand IMO. They came out with a bang and kept on keepin on.
PS2 - The saga continues. They have a much more difficult machine to code for, but they make up for it by being the only game in town as Sega can't float financially. Being aggressive on experimental and fringe titles pays off with the uber hit - GTA3.
PS3 - Aside from their 1st party titles, they have lost much of their exclusivity. Games which were born and raised on the PS platform are finding life on their competition. More of the same is likely to continue.
Timing-
PS1 - They weren't the first on the block, but they weren't far behind either. Saturn surprise launched a few months early but with limited fan fare as nobody knew they were coming and their games selection was lackluster at the time. PS1 came with a major ad campaign and the right games to show their advantage. They continued to build their momentum and by the time N64 launched, it was a done deal as they could then reduce the price and hit mainstream.
PS2 - Again, they weren't first on the block, but it didn't matter as Sega wouldn't survive the game much longer. All that mattered is they beat N and newcomer MS to the field with enough time to cost reduce and drop price on schedule to hit mainstream a year and a half (2) after launch.
PS3 - Late to the party and equal footing with Nintendo for the first time but going a against a much different company and a much different (and profitable) product.
Hype/Marketing-
PS1 - Perfect ad campagn to coincide with an impressive machine and an impressive and growing library with diversity and quality not found anywhere else. It would have sold itself, but the cool factor established by the ads helped secure it's footing.
PS2 - The hype for this console was out of control. Sony shifted into overdrive and steamrolled Sega and their DC before the PS2 even launched. The product unveiling left much to be desired considering all the hoopla, but that was just a speedbump as the built-in/free DVD player and soon to be released Gran Tourismo would dispell any doubt of it's value and ability.
PS3 - They hype and hoopla backfires as the gaming press and consumers alike are a bit skeptical given the claims and reported price. The truth is unveiled, but some to this day still refuse to believe.
PS3 will be lucky to see half the sales of ps1&2. If one of these measuring sticks were off, I could see such optimism. But pretty much all of them are.
It's not just price ... it's competition, games, timing, and marketing that have prevented and are preventing a similar sales ramp to ps1 and ps2.
Whether one calls this performance a failure or not depends on what one expected. IF Sony is able to establish Bluray with ps3, then they may have done exactly what they set out to do and rake in the cash from movie sales. I don't think Sony has any genuine target near as high as ps2 or ps1 sales at this point. Coming in a close 3rd would be a good show in the games space and squeezing out HDDVD may be all they were intending in the first place.