Technically the differentiation isn't cost reduction its in shored manufacturer. That can become an important requirement as firms become more wary of IP theft and other issues.
Besides other than that what can you really differentiate in this field that isn't cost? Its a service that is standardized regardless of country. Maybe you can provide different "styles" of boards (ie. different specs) or improve the entire submit to production pipeline but thats about it.
Consumer hardware like the iPhone would not do well when the next model is 20% slower with a 35% retail price reduction.
>what can you really differentiate in this field that isn't cost?
Don't worry about it... =3
The pipeline is a massive one - especially for PCBA. Being able to get an instant quote and order in 5 minutes is worth a lot. Nobody wants a 2-week-long back-and-forth with sales and engineering for a basic prototype run.