For the long run more disc storage is needed for impressive high definition games (The PS2 already maxed out DVD with less demanding 576i graphics and lower quality less demanding sound, already even for Metal Gear Solid 4 sacrifices had to be made to fit on 50 GB disc). Techical benefits, far more storage space, constant predictable streaming speeds for games, high definition Blu-Ray movie support and mandatory scratch resistance. Disadvantage costs.
Long term advantages for Sony by including Blu-Ray drive in the PS3, high definition movie format war is already over (far faster than anticipated), more reasons to buy a HDTV due to more and better high definition content (games and Blu-Ray movies), mass production of Blu-Ray drives and discs reduced the production costs.
The Cell also does and will show its worth. Short term disadvantage, radically different regarding some aspects compared to other CPU designs (requiring game engine redesign), benefits include again radically different approach and thus much higher potential performance for games developers to tap into for multiple purposes. The CPU provides an extremely good performance per Euro / Watt ratio.
The PS3 is just ahead of its time, yes there's a lot of technology in there like Wi-Fi, BlueTooth, default harddrive, Blu-Ray drive, Cell processor / more expensive low latency main CPU RAM, enormous internal bandwidth, etc. But due to this it should also allow the device to survive longer than either PS1 or PS2 with such high specs. Selling a PS3 specced device 2 years later will probably not have improved potential lifetime sales. It would take longer for developers to adapt their game engines, it would have taken longer for production costs to drop, it may have benefitted PS2 sales, but the Blu-Ray / HDTV attractiveness for consumers would have been far less at this point as well.
To compensate initial costs, the profitable PS2 still performs pretty well for the lower end market (while the PS3 is sold as a high end product), which wouldn't be the case if it was discontinued like the GameCube and XBox. Blu-Ray movie and additional Sony Bravia sales.
The inclusion of the latest state of the art technology also allows for more hardware cost reductions through R&D. For example Sony already developed a much cheaper slimmer Blu-Ray drive. Price is an important factor, but the PS3 already has a healthy install base and games will become more impressive and pricing will drop.