Wade's rules applied to metallic elements

There are many examples of metallic clusters that distort from the structure predicted by Wade's rules to a more 'spherical', closo-like arrangement. For example, 


1. $\ce{Bi8^2+}$ is a square antiprism (WR predict an arancho-derivative of a bicappped square antiprism, with 1 capping and 1 adjacent to an open-face atoms removed, instead of 2 capping atoms)
2. $\ce{Bi9^5+}$ is a tricapped prism (WR predict a capped antiprism)
3. $\ce{Ge8R6}$ is a square prism (WR predict an arachno-derivative of a bicapped square antiprism)
4. $\ce{Ge9R3^-}$ is a tricapped trigonal prism (WR predict a capped square antiprism, i.e. expect nido but get closo)


My lecture notes (not available online) say that 



> 
> Wade's rules are much less effective at predicting structures of metallic elements because intact polyhedra (spherical arrangements of metal atoms) tend to be a lot more stable for the more metallic elements, as compared to boron.
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> 
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Could someone please explain why intact polyhedra are more stable for these elements. 


