An interesting observation. My bog standard petrol C350 has a quoted time of 5.9 seconds to 60mph. Only 0.3 seconds quicker than the same year C350 CDI but still quicker. Then on to 100 mph it must be a larger gap because of the diesel's lower power and heavier weight having to compete with the greater number of horses that come into their own at higher speeds with the petrol engine. So perhaps the "breakfast" you talk about is a few cornflakes enjoyed between 10 and 40mph where the diesel's turbo-assisted torque will see it catch then briefly pass the petrol? Indeed, when that turbo (or turbos) lag is eventually taken up you'll get a very satisfying kick in the back - a bit like a chilli in your cornflakes? This is obviously what a lot of people want. But my bacon and eggs breakfast will give me what I prefer - sustained pleasure.
Basically I don't think it's so much about the numbers as how those numbers translate into driving pleasure. But interpretation of that pleasure is akin to the enjoyment provided by Guns N' Roses' "Sweet Child O' Mine" and Carl Orff's "O Fortuna". Both fantastic in their own way, yet so very different. Some of us want rasping staccato rushes of adrenaline whilst others want refined and powerful consistency. The end result of the time it takes to get from A to B may vary little, it's how that journey is delivered that matters more to car lovers like us. Nobody can rightfully claim that one is better than the other, just that personal taste dictates choice.
Anyway, pure performance comparisons are meaningless because there are far too many mechanical variations to be factored into the equations. Can you really compare a turbocharged engine with one that's normally aspirated? And what about the influence the heavier diesel lump at the front will have on cornering stability? Could it even be argued that the diesel's far superior torque can be a disadvantage on slippery surfaces where the higher twisting forces are very much unwanted? No engine comparison is like comparing eggs with eggs.
I guess it's all comes down to what you're used to, which usually dictates your preferences. So to return to my earlier food metaphors, most people who crave beef-burgers and fries with a Coke would chose them over beef Wellington with steamed baby potatoes and asparagus washed down with an elegant merlot. Many others happen to prefer the latter. Neither is right or wrong.
But all that, and posts from others here, still doesn't answer my question about why manufacturers don't map their cars during manufacture. Could it be that they try to get the best compromise between performance, economy and reliability? If so, as a result of spending billions in development, isn't it logical that during post-production mapping one or more factors will suffer whilst improving others? Of course the companies will refute this or they'd go out of business, so they provide lots of impressive figures and graphs. If that's what customers want then that's fine - or is it? That's what VW (and many others) did with their emission test results!
