Many old cars had spring gators to keep the grease in and the dirt out.
Some of the really fancy cars had automatic chassis lubrication systems, oiling the leaf springs was a part of that system.
I've even got a little tool made to force the leaves apart so you can get grease between the leaves.
Now that I think of it the rear spring on a 30's ford car had a center pin designed with a grease fitting and grooves in the springs so the grease would travel all the way out.

So, greasing springs in some applications (cars) was thought to be a good idea at one time.
Not so sure the same applies to trucks though, as crenwelge pointed out.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-