There is such a thing as too much choice that's for sure and I reckon that must put people off.
However once you decide on a family (in my case LPC) the chips are actually very easy to use, well the smaller ones anyway. The ability to MUX functions on pins is good and bad, I find that with a large chip (144 or 217 pins) I need a spread sheet to keep track of what function I have on what pin, that can quickly get to be a nightmare.
But as I say the smaller chips are pretty easy to work with, I downloaded LPCXpresso and had a working test program running in minutes.
Once you get your head around a particular family you are right, but if you flit from vendor to vendor you will go nuts.
Truth is the fact that there's an ARM core is irrelevant to most people, it's the peripherals that you deal with and unfortunately they are all different.
FWIW I think the SAM used in the Due is about the best chip in that size, it has some neat features that the Due does not use. But I prefer LPCs because they have a larger range so that what I learn will be largely portable from 8 pins to 217 pins. If I get a Due that will mean learning a whole new set of peripherals (or keeping to high-level code).
Rob