B + tree all the KEY in the leaf node, B tree KEY in addition to the leaf node, there is also a not a leaf node,

On one of the strengths of the B + tree than B tree many BBS blog:
Because of B + tree only keys are stored in the internal nodes, not to store values, therefore, a read, can get more keys in memory pages, is beneficial to more quickly find the narrow scope,
Or:
The interior of the B + - tree nodes and no pointer to keyword specific information, so its internal node relatively smaller B tree, if you put all the same internal nodes keyword in the same disk block, then disk blocks can hold is, the more the number of keywords,

Is also a group of data, B tree all the KEY nodes are stored, only leaf node B + deposit, it is a leaf node belongs to the extra space? Why B + tree can accommodate more key?