Memories decay exponentially. This occurs both over time and over number of items to remember.

That is a popular model, but one I find does not match my own experience of memory at all.

Sometimes just a particular smell is able to bring back a memory from decades ago of a small and insignificant happening that I haven't recalled for many years.

Certainly there are some individuals who absolutely do not fit into your characterization, and there is a lot of reason to suspect that the rest of us also can have access to that kind of remembering.