I think it is partly to do with what the artist is trying to communicate in their work. For example, on looking at a 'great' painting, you are stirred to a lot of emotions and thoughts, as well as simply admiration for the techniques. So it is not just that the artist wants you to look and say 'see how well it's made!', but s/he wants you to feel something else, something that is beyond that but more like an emotion that s/he was trying to communicate. And this could be done through any medium - it could be a 'traditional' oil painting, or a carving, or a building, or a piece of sewing, or a stage performance, or a matchstick model...
So, something that is traditionally thought of as 'high art', such as an oil painting, could actually be 'just craft'. If it's a boring, unmoving work which only serves to show off the painter's skill in putting paint onto canvas to replicate something, then maybe it's a great example of craft, but it isn't 'art'. On the other hand, a shop window display that is not just a collection of objects but a scene that strongly evokes emotions and atmosphere in its use of depth, colour and composition, is more a work of art than the well-crafted painting.
Does any of that make sense at all?!

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