Need indexes on empty tables for good performance ?

I've read that indexes aren't used for COUNT(*) and I've noticed (7.3.x)
with EXPLAIN that indexes never seem to be used on empty tables - is
there any reason to have indexes on empty tables, or will postgresql
never use them.

This is not as silly as it sounds - with table inheritance you might
have table children with the data and a parent that is empty. It'd be
nice to make sure postgresql knows to never really look at the parent -
especially is you don't know the names of all the children ..

Thoughts ?

thx,
Rohan