Just as a consideration, every argument that could be made for the PS3 being the "Longest Lasting" console with the most appeal after the next generation begins could also be made about the PSP; and right now, after 5 years on the market, the PSP is the system with the largest year over year decline (over 30%) and has less games with a release date set before the end of the year than the Nintendo DS has for the end of July.
At the same time, people constantly argued that the PSP would receive huge boosts in sales due to price reductions, and it would have been under $100 by the time it had been on the market for six years. The "huge" boosts in sales never happened because the PSP only (really) appeals to a very narrow demographic in any large numbers; and the price reductions never were as fast or as large as people expected because it is much easier to develop a inexpensive with good performance per dollar than it is to reduce the cost of an over-engineered "powerful" console.
When you factor in that the PS3 is tracking behind the PSP in Japan and North America, and is (basically) keeping pace with it in the other regions, I think it is fair to say that it will be a challenge for the PS3 to do as well late in the generation as the PSP has; and for the PS3 to last as long as the PSP will would be very unexpected.
