Tax avoidance makes more sense than any other speculation in this discussion.
Were IKEA organized as a normal for-profit venture, then anyone with half a brain at IKEA would see the utility of IkeaHackers and do one of a handful of things:
1. Buy them outright.
2. Obtain favorable advertising terms in exchange for licensing (eg, ikeahackers gets to keep running ads, but 50% of the spots must be filled with IKEA adverts, and sales-active links to the official items mentioned in each article must be included).
3. Think they're cute, and provide gratis branding coaching (including direction on proper use of their logo, precise color usage, etc) in exchange for disclaimers, and big, obvious links back to IKEA.
4. Sign an exclusive advertising deal: ikeahackers.com gets to keep operating, but must only carry IKEA adverts, with some affiliate payment structure for completed sales that originate on ikeahackers.com so that the site can continue to live on.
5. Similar mutually-beneficial arrangements . . .
IKEA have an enthusiastic fan base who, inspired by reading the blog, will likely go out to buy more IKEA product. This is not just a good demographic, but a great big juicy one. These are the people they *want* shopping in their stores, the people they *want* to reach through media campaigns.
So why turn them away? The only conditions that come to mind are when bringing the web site into the fold has larger, more threatening implications to the corporate structure, as the parent post suggests.