There is a big difference between memory and other resources, and that is that memory -- like processing -- is fundamental for any computation; not for nothing

There is a big difference between memory and other resources, and that is that memory -- like processing -- is fundamental for any computation; not for nothing do most theoretical models of computation assume unbounded memory. Very few languages require manual allocation of processing -- even though that is done in some software like OS kernels and hard realtime applications -- and for similar reasons automatic memory management is very useful for abstracting computation, i.e. not leaking their details of memory by a subroutine to its clients just as this is rarely done for CPU use. So while every non-trivial computation involves some non-constant amount of processing and memory, I/O is usually done at the edges of the system. Management of I/O is very important, of course, but it's not as central to the notion of computation (and therefore to abstracting computation) as processing and memory.