Medicine: doctors already use laptops for exactly this. Doctors also do lots of data entry (note, scheduling tests, writing prescriptions, etc), so the ability to use a keyboard is required.
Last I checked, the iPad has a keyboard dock for data entry, so if you want to use a keyboard, that's not a problem. Also, the form factor is far more convenient for use at the bedside, plus it likely will fit in the average lab coat pocket (something many netbooks don't even do well due to their thickness). If Apple is so good at making innovative user interfaces, why not make an interface that makes doing the things you mentioned (ordering tests, writing prescriptions) as easy as if the doctor had a paper chart in front of them? Laptops also have an inferior screen to the iPad, ever since Lenovo stopped using the iPad's screen technology in their laptops.
Manufacturing: to be useful on the manufacturing floor or shipping dock, it absolutely must have a camera/barcode scanner.
Not a problem - bluetooth compatible cameras and barcode scanners are available and are not very expensive. Ruggedizing an iPad like many medical companies have with the old Palm units (and adding a barcode scanner to them) for use in patient identification and blood glucose tracking shouldn't be very hard, but again, Apple hasn't partnered with anyone to make it happen or even suggest that it would be possible. They need to stop being so content with the affluent home user market and prepare a full-on assault in these left-behind markets.
Again - thinking INSIDE the box keeps you from seeing the true potential of these technologies, just like Apple.
All the simple programs have been written.