Inspired by Café Hayek, I want to muse on an explanation:
I didn't work for any of those two big businesses and have never worked for them. A friend of mine worked a few days for Walmart but quit his job due to differences with the companies philosophy. It wasn't the profit-making that upset him, but rather the intrusion of Walmart policies into private affairs and also the McCathyism of the lower levels.
I still believe he exaggerated this a big, but it might also be the difference between Ikea and Walmart. While Ikea is certainly a big retailer for wooden furnitures and Walmart is one of the biggest enterprises in the world (an Idol to Globalism and Capitalism and therefore a perfect target for socialists), the first is left alone and Walmart has been attacked relentlessly for years now. It can't be the success, because the owner of IKEA is one of the richest men in the world.
So, I identify two possible issues. First, it is an American Capitalist Big Business and as such a major evil for any socialist and European Anti-Americanist. However, this wouldn't hold up for US complains and there is much argueing going on in the American Left against Walmart. Therefore I think that the code of conduct in the Walmart business is the single point left that may raise such negative comments.
On the other side, it could well be that IKEA is left out because nobody knows of its success and everybody loves swedish meatballs ;)
You can't hate something where you are eating stuff you don't know the origins of.