Usage Statistics from ACM Library and Institutional Repository

Looking at details of (mostly) my papers in the ACM Library I find information on the number of downloads. How do these compare with the downloads for the item in the University of Bath Opus repository, I wonder?

Paper Conference ACM Downloads
(12 months)
Opus Downloads
(from 1 Feb 2010-31 Jan 2011)
Developing countries; developing experiences: approaches to accessibility for the real world W4A 2010 33 109
One world, one web … but great diversity W4A 2008 179 41
Accessibility 2.0: people, policies and processes W4A 2007 354 138
Contextual web accessibility – maximizing the benefit of accessibility guidelines W4A 2006 277 21
Forcing standardization or accommodating diversity?: a framework for applying the WCAG in the real world W4A 2005 115 41

It should also be noted that prior to uploading these resources to the University of Bath Repository the papers were also available on the UKOLN Web site.  It seems that the usage statistics will have been fragmented – although having the content available in a number of places should have enhanced access and the impact of the ideas presented in the papers.  Is such diversity to enhance access and impact to be valued more than having accurate statistics of the numbers of downloads, I wonder?