Yes if you knew the number of iPad 5s that people in each city in the world were going to buy in 2years time you could scale the production in advance and it w

Yes if you knew the number of iPad 5s that people in each city in the world were going to buy in 2years time you could scale the production in advance and it wouldn't matter how many delays there were in the supply chain. Since you don't know the demand - you need a responsive, high bandwidth, system. Having suppliers that can't respond quickly - either because they are a 2week container ship voyage away, or they take 3months to respond to quote requests, or they think they can make more money by demanding huge penalty clauses for any changes in order - all these add resistance and slow the response. There is also a cost consideration. Once you start making a component it is costing you money until the consumer pays for it. Having to make a billion $ worth of screens/chips/cases 2 years in advance is costing that whole network of suppliers money - costs which will be passed onto the customer