First I should say that we switched our developer goals on a new Chart engine for Silverlight which was released with Q3 2011 - RadChartView and all our efforts were and will be mainly in this Data Visualization control.
Onto your question - indeed there is no such way out-of-the-box to have reverse YAxis but there is a workaround which you may want to use. You may find a discussion on the matter as well as a sample project attached in this
the Telerik team
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