More on 'Many' and 'Few'

It is well-known that sentences containing 'many' and 'few' are in some way context-sensitive. Consider, for instance:

(1) Few German linguists applied

If the topic of the discourse is last year's applicants compared to this year's applicants, then we would tend to interpret (1) as meaning that few German linguists applied this year compared to last year. Here is another example:

(2) Few philosophers have a blog.

Compare: "few philosophers have a blog. The rest are doing more serious work" and "most linguists have a blog, but few philosophers have one". In the first case (2) gets read as "there are few philosophers with a blog compared to philosophers without a blog". In the second case (2) gets read as "there are few philosophers with a blog compared to linguists with a blog"

But what exactly makes sentences with 'few' and 'many' context-sensitive? Are 'few F' and 'many F' indexical in a broad sense? Are their extensions contextually variable but their contents contextually invariant? Or does the context-sensitivity simply reflect a difference in what the sentences are used to assert?