Thank you, sir. Harry Balzac is correct. Kamui is the same for both Kakashi and Obito, they obviously have just learnt the MS techniques differently Kakashi's primary use of it is for the dimensional transportation of objects, whereas Obito tends to just teleport himself.
It could be that Madara is just stronger and therefore able to use it, however, I believe it's a little more complicated than that. I think that it could have something to do with the tree... But that is a big maybe. On the other hand, the reasoning behind why Obito was unable to use Kamui could come back to the fact that the Juubi was huge. Obito might not have had the eye prowess to perform such a task, whereas Madara's power and visual prowess is arguably infinite. Conversely, the Juubi might just not be able to go to the other dimension for whatever reason. It's all subjective at this point until Kishi explains it (which he may not even do, but hopefully he will).