Some of the studies seem to control for this. Some have looked specifically at isometric vs eccentric, etc and found the isometric grip strength exercises to be more correlated.
On a side note, there have been studies about grip strength and lifespan, including on small children who have never strength trained at all. Higher grip strength had a fairly strong correlation with longer lifespan.
On a side note, there have been studies about grip strength and lifespan, including on small children who have never strength trained at all. Higher grip strength had a fairly strong correlation with longer lifespan.