There is a very strong chance, that all 10,000 parts kits will make it through manufacturing, and become fully baked Pis. Likewise, most shipments make it from China to the UK without incident.
Sometimes things go wrong. If the thing that goes wrong is a systematic error, then it will go wrong the next time.
The Foundation wants to have tested Pi's in their hands, before they start taking orders. If it turns out that they have significantly less than 10,000 systems to sell, despite expending the capital to produce 10,000 systems, then issues will have to be addressed before hitting the big red switch for the next batch.
In the more likely situation that things work well, then close to 10,000 systems will go up for sale.
A week or two later, a significant number of customers will have the systems in their hands.
Some percentage of customers will have issues and need some level of customer support. Some customers may need replacement Pi's due to shipping issues. Some customers will want their money back. The financial types will want to know those percentages.
If things look good in the first week or two, the financial types will probably let the Foundation hit the big red switch a few more times on more 10k unit orders.
Assuming the Foundation's clerical staff isn't overwhelmed after several weeks of products in the field, and the post office only chews up a tiny percentage in shipping, and hardly anyone wants their money back, then we will see the Foundation ramp up production.
If things go incredibly well, the Foundation can get financing for massive production. If things go moderately well, the Foundation can have the Pis produced in moderate volume, or they can tweak things until things go incredibly well.
Hopefully, sometime around April or May, the Foundation will need to know the demand level, so they will know if they should order 500,000 or 2,000,000 units per month. Up through at least March, we know there will be sufficient demand to soak up as many model B's as they can sanely make and sell at $35 each. We won't need to be counted.