Kefuddle - the regulation, CAT.POL.230 (f), relates to one specific situation whereby your LDR is longer than the most favourable runway in still winds. Why does this preclude a wet runway? It could be a runway that becomes limiting when wet, and the only way LDR could be met is with a favourable wind condition, calculated using all the restrictions laid out in (a) - (d). In this extraordinary situation, you require a second alternate.