lol-we both know there's more to it than
that 
(good support doesn't come cheap and the extra features and packages are superb)
While every company has feature request lists - the nice thing about the process here is that you get to track the work being done; other companies just hide your RFE's in some unseen database, or "coming in version x" list. (though PMWeb does that for us here too)
Think of all the material they've given away! Of the overall code about 90% written by Zimbra and released in the OS edition, 5% written by non-employees, and 5% retained functionality for various levels of paying customers =95% of the product given away for anyone to modify. Then look at exchange, groupwise: nada zilch (and they cost even more)
People have designed whole businesses using the OS edition, and zimbra might never see a cent for their work-now
that's pretty damn generous.
And it's a conscious effort (plus a good business model obviously-especially in the area of OS to NE converts) but it makes you wonder why more don't do it. Think of microsoft, they gripe about pirated copies of windows, yet at the same time hand it out free on college campuses (to get students hooked for later I might add) but talk about a glaring catch 22.