9.2 and index only scans

Hi,

I'm playing around with 9.2 beta4 and was looking into the new Index Only Scan feature.

I was a bit surprised that a "count(*)" query does not use an index.
Not even a count(col) where col is the PK of the table.

Is that intended? If so, why is that the case?
I would have thought that this is an operation which is suitable to be served by an index only scan.

Regards
Thomas