As I see it, the Network edition offers enhanced functionality and formal support contacts, both essential in many businesses.
The enhanced content is pretty much a one-off development cost for Zimbra, once they have wrote the code, it's sort of 'done'. The support is the real cost to them, and I think it's what the main part of the license pays for.
So here's my take on it: It stands to reason that the less times a customer contacts zimbra for support, the more money they make. Obvious really. Two customers purchase a 200 user license, one customer never calls for support, one is on the phone every week, one of these customers is costing Zimbra money.
The reason the first company never phones for support may be that the local admins know what the are doing, so My suggestion is that when a company purchases a license for the business, a further license is issued so the administrator can run a system at home as well (or a small development server at work) this allows the admin to learn more, to take risks with the home/dev system that they cannot with the production one.
The greater the local knowledge, the less support calls and load on the Zimbra support team.
So while I appreciate that it's not cost effective or desirable for Zimbra to issue licenses for less that 25 users at a time, I think that a second 'development' license, limited to 5 accounts could be something that would actually make money for zimbra in the long run.
We are currently running OSS at work and we are looking into switching to NE, I also run zimbra at home. Guess how much harder I'll push the business to purchase NE if I get a free copy for my home install
Food for thought.