I mostly agree with all this -- I remember the glee with which people would discover and report "undocumented" BIOS or DOS interrupt calls, and the feeling that Microsoft were holding back on documenting these calls for selfish reasons -- but I can't see how they caused the 640k limit. That limit was built into the segmented memory architecture of real mode 8086 and successor CPUs.
The limit wasn't insurmountable. With segmentation, the CPU had an address space of 1M, but video memory was in the middle of it somewhere, limiting the possible size of the contiguous address space usable by programs. There were some work-arounds, including machines that added a few more k, IIRC 786k.
Improving matters would have required some coordination among software vendors, or authority from the OS vendor, neither of which existed. Part of the reason for the "closed box" approach of the Apple Mac was to prevent this from happening. My friend described it thus: "If you break our rules, we will break you in the next OS release."
Today it seems like such a tiny amount of memory to squabble over. We waste that much memory without batting an eye.
