From what I remember it was more to do with weapon construction. UK 1000lb bombs were (are still) forged and are swaged from a single billet. They are capable of penetrating further than the US Mk 80 series which are cast - better for fragmentation but poorer penetration capabilities.
On a number of missions the Buffs used the UK 1000lb as an airfield denial weapon as it was capable of penetrating the operating surfaces and generating greater heave.