Skins made of material of high ' Modulus of Elasticity ' are best used in conjunction with cores of high ' Shear Modulus '. This balance is important so that neither material fails long before the other is stressed to acceptable level. Of course, for this reason Styrofoam is not considered a structural core material. It also shows superior compressive and bonding strength to the skins. Of course, it doesn't mean that it is the best choice in all situations.
Some cores are less stiff which makes for better impact absorption.
The point here is that despite advances in material science, the 'Good old wood' is still up there with the most sophisticated materials used today. As far as cedar wood strip core is concerned, it has its own unique advantages that no other core has. All commercial cores need close spaced forms or solid surface plugs so that they don't sag. No special skills or tools are required to build a professional looking kayak with wood strips. The Wood Core Kayak page goes into more detail about its virtues.