Jwscud,
Those figures are guidelines rather than hard rules, and operational commitments may well mean those guidelines are routinely breached.
Added in to that, I suspect the RAF figures are now out if date given that the NFU tour length has been standardised at 6 months - with the usual amounts if separated service each year on top of that figure for un established commitments, Ex, trg etc. So if you were to compare the Services over the exact same length of time, I suspect there wouldn't be much in it between any of them.