It's incumbent on IKEA to police unauthorized use of their trademark somehow, but that doesn't have to mean that they must start by sending a nasty letter. When Jack Daniels thought their trademark was being infringed, they started by sending a nice letter simply asking the infringer to stop.
Another way to deal with unauthorized use of a trademark is to authorize it. So IKEA could have started with a letter asking IKEA Hackers suggesting a potential agreement and a nominal fee. An imperative cease and desist letter isn't required.
The Jack Daniels C&D letter should be a case study in public relations. While not universal, people really do respond quite well when faced with civility and respect.
http://abovethelaw.com/2012/07/cease-and-desist-letter-of-th...
Another way to deal with unauthorized use of a trademark is to authorize it. So IKEA could have started with a letter asking IKEA Hackers suggesting a potential agreement and a nominal fee. An imperative cease and desist letter isn't required.