IDA Systems

Short answer as an end user: because I want to be able to fix, modify or add to the stuff I buy, not rely on the whim of the manufacturer.

Longer answer: Products are rarely exactly what I want, and I'm not afraid to modify them to get what I'm after. Access to mechanical and electrical design documentation makes this both easier and more effective. With software-based products the openness is more necessary. My TV contains some GPL software, but nobody has worked out how to build a complete firmware image, let alone load one, so I can't readily fix any of the niggles or add features.

Also I hate arbitrary limitations and designed obsolescence. Phones are a good example; why should I need to buy a new handset to get a feature the existing hardware is capable of, and supposed to have, but doesn't because of botched
firmware the manufacturer has decided not to fix? Why is this simple software feature only available on the 'pro' model at 3 times the price, or not available at all?

Finally I find the faults somehow less irritating when I know I could fix them if I could be bothered.

Small scale commercial answer: because custom software on an existing open platform can make small market niches commercially viable when they wouldn't be otherwise

What is Open Hardware/ Qi-Hardware?

It is a product that follows the following guidelines: 

• Copyleft Plans (CC BY-SA): Free plans to manufacture the device
• Copyleft Software (GPL): Open software used on the device
•  Copyleft Patents (Open Patents): Patents free and clear for technology on the device