Rewritin' history: it depends where you start

From the BBC:

The number of MRSA infections in hospitals in England has fallen by 40% compared with the same period last year, figures show. Between April and June this year 509 cases were reported, compared with 839 in the same quarter in 2008, the Health Protection Agency said.

The latest figure is a quarter of the peak of nearly 2,000 in 2004. Rates of Clostridium difficile infection are also continuing to fall with a 37% drop from last year. The government met its target to halve 2004 MRSA rates in summer 2008, and at the time ministers called for the NHS needs to focus on sustaining the reduction.

What's the significance of 2004? What is the relevance? Ah ... I see:
Chart from National Statistics Online. OK, that's deaths not cases, but I'd assume that the two move roughly in line. It's not clear to me why they chose 2004 rather than 2005 as their 'year zero'.