Ahh ..
Well to clarify the hardware device is only a smallish part of a bigger picture.
I work like this .. client has a problem, I propose a solution and demonstrate a prototype with cost estimation. If the client is happy with the proposal I source whatever is needed and provide the rest. The client is not concerned with the details. (This applies to all my projects, electronics included or not)
The reason why arduino features here is because at the volumes indicated I don't think its worthwhile designing a whole new Atmel based board AND the programming side of the arduino suits me. It also breaks down to a modular approach which I prefer.
Of course I could have gone the another route e.g. outsource even the prototype to 'professionals' but that route often proves to be expensive and slow ... and .. I'd rather support the open source community. 