You're absolutely right that being "most powerful" has never been an indicator of anything. PS1 was MUCH less powerful than N64, for example, yet N64 got trounced. Xbox 1 was clearly much more powerful than PS2 (the first Splinter Cell game was *dramatically* better looking and playing on Xbox than PS2), yet it got trounced as well. PSP is WAY more powerful than DS, yet again--got it's ass handed to it. People love specs, I believe, because they're measurable, even when the specs we get don't always reveal useful numbers.
A case in point was, of course, the Cell processor. According to Sony's released numbers it was roughly twice as powerful as Xenon, yet 5+ years into this generation and we've seen no real evidence to demonstrate it. On the contrary, more often than not cross platform games get the better deal on 360, with higher resolutions (albiet, very slightly), better AA, better framerates (look at Skyrim between the two platforms; gorgeous in both, but in certain circumstances the PS3 version chugs to virtually unplayable framerates) and so on. Goodness knows there've been plenty of flame wars on the matter, citing figures, and if you go just by the released numbers then sure--PS3 is dramatically more powerful. Unfortunately, few ever acknowledged the mitigating factors: PS3's split memory, two different kinds and speeds of memory, SPU's inability to directly access memory, 128 bit system bus and the generally slow transfer speed of 2x Blu Ray all conspired to mitigate those raw numbers. That's why it's really importnt we never take published, raw numbers at face value; they're selected only to convey the *marketing* message the corporation wants you to believe. Lacking specific knowledge of how computer systems work, most people will simply interpret "higher number=better," but that's not always true, as we've seen.
I like to highlight, though, that whether PS3 or 360 was more powerful than the other or not, both have offered a very healthy serving of great games. At the end of the day, how much has it really mattered whether one or the other was more powerful? My take is: not much at all. As long as the games are good games, that's all that matters. And now that we've reached the era where PS3 and 360 are our baselines and HD is expected, there aren't going to be any more ugly games (barring artistic style preferences, of course :P) going forward. So, I'm not at all worried about how powerful the next systems are.
I'm in truth very happy with both my PS3 and 360--and often, even my Wii. Knowing that anything that comes after this generation will be at least as good looking as typical 360 and PS3 games, and possibly even better? I can live with that :P