For practicality reasons, an external USB keypad is less convenient than a built-in one. A keypad is required for entry of lots of numbers, and using the alpha keys with the Fn key to turn them into a keypad is not acceptable.
Looking at the larger manufacturers, it seems that none of their business grade laptops (e.g. Lenovo's T-Series or similar quality levels) have numeric keypads. Looking at their laptops that do have keypads, invariably they are cheap, plastic and flimsy. Looking at Lenovo's offering with a Keypad, whilst it's a 15" screen, the vertical resolution is just 768 pixels, and the build quality of it leaves a lot to be desired.
I need to find something that is built to the quality of a "real" ThinkPad, or even a MacBook Pro, but has a full-sized keyboard with a numeric keypad and there doesn't seem to be anything like that on the market at the moment. This is a mystery to me as to why it would be the case as I'd imagine it's business users who need to use a keypad more than the average user, yet it is the consumer grade laptops that have keypads."