It's that a new computer design which disregarded all the familiar tenets of personal computing unexpectedly became a major platform. The mouse was replaced with a touchscreen. The decades old metaphor of overlapping windows shuffled around like papers on a table was replaced by apps that owned all the pixels of the device. All those years of learning the intricacies of the Win32 API no longer mattered; this was something else entirely. And most significantly for our purposes: the CPU was no longer an x86.
I just really love this kind of thoughtful perspective from recovering programmers. James has a lot of good stuff.