This is very true - it can rain a fair bit and still not cause the mudbath that we all so want to avoid.
I am still reasonably optimistic - a 6 or less on the dustbowl to washout scale is perfectly acceptable to me. If it gets worse than this then pack full waterproofs. Wellies, waterproof trousers, jacket and hat. This can turn a miserable festival experience into a bearable one. I won't tell fibs, it may still be a bit of an endurance test but it will be preferable to sitting in an office all day.