Learn English – Head nouns in ____ of ____ noun phrases

For me, this example shows a limitation of the concept of head noun.

@KSHuang asks the intelligent question, which of the following is more "grammatical?"

a) "Lives were lost." b) "Thousands were lost."

Both the examples are perfectly grammatical. The only difference is that as a noun phrase "thousands," playing a pronominal role in "Thousands were lost.", can be thought of as lower status grammatically than the noun "lives."

What is really going on here is that, in the absence of context, more meaning is carried by a) than by b). In terms of meaning, clearly a) is the better approximation to Thousands of lives were lost.

So my answer is first of all to question the usefulness of the term "head noun." However, if you are going to use it, I suggest that you need to assess it on the basis of lexical weight or meaning.