[boost] [MultiIndex] Why do constructions of multi_indx_base_type<> and multi_index_node_type<> differ?

Hello, I have a question about implementation details of MultiIndex. The type multi_index_base_type<> is created with the metafunction nth_layer<>, which in turn uses mpl::eval_if_c<> and mpl::apply2<> to build the type by recursion. The construction of the type multi_index_node_type<> is very similar, but it is implemented in more succinct way using mpl::reverse_iter_fold<> and mpl::bind2<>. I am trying to find out whether there are reasons to keep the more complex construction for multi_index_base_type<>, your input will be appreciated. Thank you Greg