Ok Wait a second here.
An archer with a readied action to loose an arrow when the wizard begins casting is allowed to attack if, and only if the wizard visibly casts a spell. The archer is fully entitled to the attack, provided he knows the spell is being cast.
This very same wizard, with a spell augmented by the Still Spell and Silent Spell, would not visibly cast the spell. Therefore there is nothing to see. There is no physical or visible difference between a slient/still spell being cast, and the wizard readying his action, unless the spell produces physical or material effects, ie color spray.
The archer, with his eyes set on the wizard sees nothing but a wizard standing still. Who is to say that this wizard hasn't readied his action to that of the archer.
Now I may be new to this board, but I am not new to DnD, and I don't remember 'zenning out' being a term thrown around in any of the official books or errata from Wizards of the Coast. You know WOTC, the guys who MAKE THE RULES.