I also am not an expert on this IPFS technology... I think unfortunately the whole d.tube thing is a little shady compared to text on the Steem blockchain, that is perfect!
I still use and promote D.tube, as I think it is (together with dlive) the best alternative we have, also because of the Steem payment model.
I was making videos for a long time thinking that they would be stored permanently, but that is fare from the case, it is more like only 1 weeks storage or so, I have heard, but not checked it!!.. The length of the storage time should also depends on the numbers of views, again this is only someone told me in a comment, I dont know if it is true or not!
I have asked Adrian (@heimindanger) a lot of questions related to this, but he only responded ones and not with full details.
So in effect d.tube is a mystery to me, but I still use it.