enough ram to run without swap file thrashing. Price was high as well
These two are related. OS/2 needed 16MB of RAM to be useable back when I had a 386 that couldn't take more than 5MB (1MB soldered onto the board, 4x1MB matched SIMMs). Windows NT had the same problem - NT4 needed 32MB as an absolute minimum when Windows 95 could happily run in 16 and unhappily run in 8 (and allegedly run in 4MB, but I tried that once and it really wasn't a good idea). The advantage that Windows NT had was that it used pretty much the same APIs as Windows 95 (except DirectX, until later), so the kinds of users who were willing to pay the extra costs could still run the same programs as the ones that weren't.
Sort of. The desire not to cannibalise sales was a key factor in the design of the PC, but these were also features that IBM didn't think would be missed.
IBM knew what multitasking was for: it was to allow multiple users to use the same computer with administrator-controled priorities. Protected memory was for the same things. Why would you need these on a computer that was intended for a single user to use? A single user can obviously only run one program at a time (they only have one set of eyes and hands) and you can save a lot in hardware (and software) if you remove the ability to do more. And, of course, then no one will start buying the cheap PCs and hooking them up to a load of terminals rather than buying a minicomputer or mainframe.