This service is rather performance intensive and therefore there is an upper limit of 20 entries per feed. This means only the first 20 entries are even looked at and all subsequent entries are not geocoded.
If this is a one time geocode job, then I can tell you the parameters required to circumvent this limit.
I'm looking for a way to get around the 20 entries per feed limit for a demo. Would be interested in learning about the parameters? With the commercial GeoRSS support, does it support more entries?