Looking up what companies are leveraging PUE or DCiE, I found this marketing document on Sun's website, Accurately Measuring Datacenter Power Efficiency.

You can tell this was written by a marketing team as there is no mention of DCiE or PUE, even though it shows this formula.

I ran a search on IBM's website and I can't find any mention of PUE except in a powerpoint presentation by Eaton.

Maybe Sun can help Google measure its data centers below 5MW.

Google says they eliminated data for facilities below 5MW.

Such a strong claim demands evidence, especially in light of recent criticism of companies "gaming the numbers." On this page we will explain our measurements in detail to ensure that they are realistic and accurate. It is worth noting that we only show data for facilities with an actual IT load above 5MW, to eliminate any inaccuracies that can occur when measuring small values. This section is aimed at data center experts, but we have tried to make it accessible to a general technical audience as well.

If we believe Google's claim that you can't measure accurately below 5MW (google's definition of a small value), then the majority of data centers have an excuse for not publishing their numbers as they can't be accurate according to Google PR/Marketing.

What is the true reason why Google excludes data centers below 5MW?

Too expensive to instrument.
Google doesn't have any data centers it built below 5MW.
The PUE of these data centers is high.
Google doesn't have good data on the data centers below 5MW.
There are a lot of less than 5MW data centers, and it was easier to talk about a few big energy efficient data centers.
Instrumentation is inaccurate at less than 5MW.