Recently we've received notification that Google annouced closing of the best cross-client reporting feature.
First they announced the feature here:
...] sying that:
Easily run reports across clients: ReportDefinitionService now supports My Client Center (MCC) cross-client reports, which are fetched asynchronously.
This feature did not go live as expected, so is currently only available to a limited set of developers. We hope to make it generally available in the coming weeks.
and now they write that:
This feature was under development and available for testing purposes only.
What is interesting, they still give hope saying:
Note: This feature is still under development and is subject to change. Future release of this feature will be announced on the Adwords API Blog.
I think they do not want to support agencies and big developers and they've cut the budget for that.