Looking at the code related to throwing, I can say that strength is used to determine range but not accuracy. It's also based on the weight of the item being thrown. The equations used as as follows:

iThrowingStrength = ( EffectiveStrength( pSoldier ) * 2 + 100 ) / 3;
iRange = 2 + ( iThrowingStrength / (3 + (Item[usItem].ubWeight) / 3 ));

So a merc with a 50 strength would have a iThrowningStrength of 66 and if this merc was throwning a "Mk2 Grenade" (ubWeight = 6) the iRange would be 15.