Thomas,
I would have to agree that the current results do indicate that. However, I have run this explain analyze multiple times and the timing varies from about 4ms to 35ms using the Bitmap Heap Scan. Here is an explain plan from Thursday of last week that shows about 21ms. Part of the issue in trying to isolate if the query can be faster is that once the data is cached any way that the query is executed appears to be quicker.
http://explain.depesz.com/s/SIX1
Thank you,
James