I think this problem goes beyond software like lotus notes and outlook/exchange servers. The same difficulty often applies to any business decision. As individual workers we can definitely see that our productivity is increased when we use an automated tool like GTD. And by productivity we mean the "work" that we produce. Thus we say that our productivity has gone up.
The challenge is that in the world of business decisions, particularly larger corporations, it's difficult to see whether or not the increased productivity is worth the additional expense. Because we were able to do more in our jobs was there a direct link to an increase in profits? Did the corporations operating expenses go down? In accounting terms, "productivity" is defined as net profit divided by operating expense. So unless either term is directly impacted by the change it's difficult to show an increase in real productivity. Just because we can do more work in less time doesn't mean that our productivity has actually increased. At least not in the accounting sense.
Most business decisions are made at the 40,000-50,000 foot level. They have to be because the decision makers answer to the board of directors and the shareholders whose goal is to make money. So unless you can show a real impact on productivity (or turns--which is net profit divided by inventory), it will likely be difficult to demonstrate to a decision maker that any additional expense is justified.
At the Runway and 10,000 foot level its often very easy to forget this.