It's one of the considerations in determining what the rate should be. It's not just the government's borrowing rate, but, potentially, what the taxpayer's borrowing rate is. Of course, that's difficult to assess, because different taxpayers have different risk profiles and will borrow at different rates. It's just one of the considerations that's taken into account when determining what the appropriate rate should be.
On October 26th, 2009. See this statement in context.