Seems like I'm running out of topics to be posted into this thread, so just some final words:
When the 6502 was invented, it aimed at small "embedded" projects from the start,
in a niche were we now have the microcontrollers.
(6530 had RAM, ROM, I\O and timer on chip, so it was possible to build a small computer with only two chips.)
From the designers, 6502 wasn't intended to end up in computers, this just had happened
because it was the least expensive CPU chip back then.
68000 was invented to compete with Minicomputers from the start, so interrupt response timing
wasn't a big issue to the designers.
From the designers, 68k wasn't intended to end up as a microcontroller,
this just had happened when applications became more complex and required more memory.
(68k showed up in early laser printers, for instance.)
You now may ask: so why 6502\65816 and 68k still seem to be there, despite ARM and 80x86\Pentium ?
To put it this way: as a human, you might be the "pinnacle" of evolution,
and it looks like designs like the shark and the crocodile haven't changed much during the past few million years.
Nevertheless, when trying to directly compete with those creatures for food in their natural environment,
chances for success won't be too good.
BTW: the 4004 also had started as an obscure calculator chip, and it didn't instantly appear to Intel
that it could be useful for any other applications.
There might be a parallel universe somewhere, in which PCs may look pretty different...