When deploying packages across many machines, it is often desirable to deploy just the client tools and libraries for use by linked applications instead of all the headers and server. Likewise, on a development machine, it may be desired to deploy just the headers for building tools that use the mongo client libraries and not the actual server or other tools. This is more in line with how many client/server/dev packages are already deployed on debian currently.

I have separated the single monolithic mongo package out into its several smaller components already:
http://github.com/shtylman/mongo

This type of packaging is easier from a server administration perspective.