The C standard was (and is) written so that it allowed for machines that didn't have simple pointers; a highly relevant example for the time was x86 machines in real or protected mode using segment registers. Even when such environments have accessible linear address spaces under the hood, comparing the absolute address of two pointers requires some extra work (you have to reassemble the absolute address from the segment + offset pair). In the grand tradition of allowing the most efficient implementation possible, the C standard says that implementations don't have to do this work; they can simply compare pointer values directly, provided that they insure that pointers to the same object work (eg use the same segment + offset pair, which they normally naturally will).

The standard was also written to allow for C interpreters, where you may not have an underlying linear memory model at all and all pointers are represented internally in some complex way (for example 'object ID + offset inside object'). Here you don't have any particular idea of 'an address' as a distinct thing and so you can't naturally compare two pointers to different objects in any meaningful way.

Because (a) pointers do not point to addresses, and (b) now you have to define the concept of addresses being equal in the language standard and haven't actually reached the goal. (-:

Indeed; pointers intentionally abstract away memory addresses and addressing, which, as the article states, can be much nastier business than the benign flat address space of i386 protected mode.