IDEs are a special case, and not necessarily representative of the platform -- they're trading memory for speed on purpose. Cross-referencing and API lookups have to be fast, memory footprint is far less important.

Something like the Eclipse RCP mail app demo could provide a more representative baseline memory footprint of the platform (http://www.eclipse.org/articles/Article-RCP-3/tutorial3.html). The Eclipse platform can be quite compact without the IDE features, JDT & online help indexing, etc.