The arduino seems popular in prototyping and customer validation of commercial products(example: the fitbit), i think some low/medium volume products are using

The arduino seems popular in prototyping and customer validation of commercial products(example: the fitbit), i think some low/medium volume products are using the arduino hw/sw(but you might not know it's there-why should the business owner tell you?), and for high volume products, standard development methods give cheaper products.