I'd say it depends on how much you consider the verbal component to be a part of spellcasting. For RM2, the Spell Users Companion offers a section on how to handle spells components, may it be the vocal part, the gesture part, the needs for some physical component, etc. in ?2.3, Magic Minutiae.
That being said, I don't think a Silence spell should affect spell casting at all. As Ecthelion said, the verbal component was performed, and audible. Sound doesn't travel in and out the silence area, but it is indeed created and the spellcaster himself hears it.