I've heard that theory before, and I doubt its accuracy.
Life like ours, out on the surface, would have difficulty living without the magnetic field, but we evolved on this planet. Life that evolves in an ocean doesn't have to worry about radiation. Look at Europa, for instance - we think it's possible for life to evolve there, and it's in a much harsher environment than the Earth would be even without a magnetic field.
If life evolved in an ocean on a planet with a dead core, and eventually left the ocean to colonize land, it would evolve the capability of dealing with the environment. Perhaps it would have extra redundancy in its DNA analog, or maybe it would not even use a cell-based system like we do. Who knows?
That said, while life might be more common than you think, you might be right about intelligence - at least at our moment in time. I would be very surprised, however, if we were the first intelligent life in this galaxy.