I'd have a hard time believing a spring would ever work it's way loose. I have had to pull them out of old hoses with pliers, and use string to help pull them back into the new hose.

The spring is so small in diameter that I doubt there is enough surface area there for the fluid to grab hold of it to any degree. Also the water pump inlet is much smaller than the spring diameter in every one I've monkeyed around with.

I'd say they stopped installing the springs because that would be one more added cost that would cut into their profit margin.....