"Just googled K1 - theres K1 phones, K1 Crankshafts, K1 Motorcycles, K1 Cameras, K1 Transceivers, K1 mountain Range .......... oh and K1 Kickboxing!"

Trademarks are established per market. That can be a gray area, but it seems that only well-established company names could claim trademark across markets, such as coca-cola. In other words, nobody could create a T-shirt company called Coca-Cola T-shirts. But (as you pointed out) there are K-1 brands outside of the sports market. Microsoft's windows brand only applies to software and technology markets. The term "windows" is obviously used extensively in the construction market.

Some teenager in Canada started a web design company called "Mike Rowe Soft" (using his name) and Microsoft won a trademark case against him to have his site taken down and his name changed.
Here is that story on Wikipedia http://en.wikipedia.org/wiki/Microsoft_vs._MikeRoweSoft