Not so much "do what I mean" as "do what the underlying hardware architecture does". For example, on pretty much any machine your code is likely to run on these

Not so much "do what I mean" as "do what the underlying hardware architecture does". For example, on pretty much any machine your code is likely to run on these days, pointer arithmetic is the same as unsigned arithmetic, and so it's quite reasonable to expect C compilers to treat it that way. The spec can't mandate this because there are some obscure historic systems where pointer arithmetic is bounds-checked in hardware or has other oddities, but people not writing code for those systems shouldn't have to deal with that.