update_frequency vs publish_frequency (costmap parameters)

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Going over to an answer now, instead of comments.

update_frequency and publish_frequency refer to the costmap for which the parameters are set.

As specified in the wiki, and as you cite yourself:

• update_frequency is how fast the costmap should be updated. I.e. how often new sensor data is integrated.
• publish_frequency is how fast the costmap is published.

note that for some applications (like move_base, e.g.) the costmap does not need to be published at all. As move_base accesses it via the API, publishing the costmap is only for visualization purposes. This is why there are two parameters, leaving you the choice to publish it, or not; publish it with very low frequency but integrate sensor data faster, or whatever you prefer.