Project Ara. Haven't we done this before with PC's?

Project Ara with it's modular upgradable components seem very reminiscent of PC's upgradability.

Point being that we can upgrade the memory, video card, and other components on the PC, but eventually when newer incompatible technologies come out, it renders the old hardware obsolete. We are then forced to discard the older hardware and start over from scratch.

One of the promises of Project Ara is for it to have a long life span, but it seem to me that like PC's there it a limited shelf life.

It's a fascinating concept. Yet, I am doubtful about it fulfilling it's promise.