Windows can distinguish between multiple keyboards. That is to say, it knows you've got two keyboards plugged in and it knows which keyboard each keystroke comes from. But you're not running an application that tells Windows to react differently to each of the keyboards, so Windows, by default, took both keyboards equally seriously. You pressed shift on one so Windows entered a shift state. (The shift state belongs to Windows not the keyboard.) You pressed a key on the other and Windows accepted the keystroke and capitalized it. If you want Windows to react in some other way you need to find an application that describes that other way to Windows. So far as I know, nobody has bothered to write that kind of application. I thought about adding this feature to HotkeyNet but decided not to because Windows's "multiple keyboard API" is missing an important capability that HotkeyNet needs.

Specialized keypads are expensive because (1) unlike keyboards they aren't built from commodity parts that sell in huge numbers and (2) specialized keypads come with a lot of custom software which often includes device drivers. Also (3) some specialized keypads are designed for industrial use and are made from higher-quality parts than ordinary keyboards.

People here tend to distinguish "hardware"" and "software" when talking about solutions that broadcast or generate output but very often it's a false distinction. The "hardware" products are actually packages of hardware plus software, and in many cases the software component is larger and more expensive than what you get with pure software solutions.