I must have misunderstood your point. I thought you were arguing that manufacturers who produces a variety of products with plants in the US and Taiwan can only afford to make their expensive products in the US because only those products have the margins to offset the relatively high US labor costs.
But from your response (and on re-reading your original post) it sounds like you're actually pointing out that high-volume manufacturers with thin margins have more trouble justifying high US labor costs - in contrast to low-volume manufacturers with high margins.