I've got one specific example, where I know the quality has changed. I've bought the same modelf of sofa about 10 years apart. Ikea has done some serious value engineering. Both sofas look very similar from outside, but they are in fact very different. The newer frame appears to be somehwhat lighter, yet sturdier at the same time. The cushions however are now lighter and far less comfortable. They obviously spend a lot of effort into making everything more efficient and cost effective - some of it at a slight cost in perceived quality.