We do have a firm idea about RBA capex expectations for 13-14 — from the Kent speech.
They are expecting a gradual decline in 2013-14. Say a headline number of 137.5b (nominal, first estimate). I think it must be materially worse than this to get a cut in March.
Post-script: as it turns out, the first estimate for capex in 2013-14 was ~152.5bn, so it looks like the capex droop may be slower than the RBA forecast.