In this question a side issue came up of whether you can cast a spell with Somatic components but no Material components while holding a focus in the hand used for Somatic components.
My reading of the rules sees "A spellcaster must have a hand free to access a spell's material components–or to hold a spellcasting focus–but it can be the same hand that he or she uses to perform somatic components." – it doesn't say you have to be holding the focus for the purpose of avoiding materials.
However, @Adeptus and @enkryptor argue that – since that rule is in the section on Material components – you don't consult it in for spells without Material, and fall back to the Somatic rule "the caster must have free use of at least one hand".
(I also appeal to the logic of fluff – why should it be harder to cast a spell with fewer components?)
Is there an official RAW or Word Of God on this matter? Can you cast a material-less, somatic spell while holding a focus in your only free hand?