everyone makes the comparison with Apple, but I find that comparison rather flawed. In my mind it is more like the way Sony use to be when it had a cohesive product line (yes, it has been a while, but they did almost have one back in the '90s), where you wanted to have the matched set of the TV, receiver, radio, CD player, DVD player, speakers, etc. And when you stuck with the Sony brand then you would have special features, such as the receiver controlling the other devices. But if you got something of another brand, those products worked just fine with your other Sony branded equipment.
I think that MS is moving in that same sort of direction, saying that 'this is the way we think hardware should be', and it all works together with the 'full expierence'. But if you purchase a product from someone else, it will integrate just fine with the other parts. Even if you move to a different ecosystem, such as Android or OSX you can still link certain aspects which are software agnostic services, and get by just fine in life. It is not the total experience, but it is still functional.
In this case you will have the WP8 Surface, Surface tablet, and the Nextbox as their desktop PC replacement. All 3 devices share the same basic OS at their heart, and all work together, but they are not a closed group of hardware like apple products tend to be. You can install smartglass on your other branded phone, and have it work with your xBox or nextbox. You can network your macbook and have access to your network files, etc. Where as in apple land you cannot have a PC read files from your apple network, and it can be a pain to sync data between your android phone and iMac, etc.
At any rate, in the end Sony tried to close the system and become exclusive, and failed miserably (at first because they could not get departments to work together, and later because of QC issues). And most other companies who have closed the loop entirely have simply been abandoned and left for dead. MS knows this, and they know that they are not Apple, and could never get away with what apple has done. And with more crap products like we see with the new iMac and iPad mini I doubt it will be long that Apple can remain being Apple as well... but maybe it is just a growing pain they will move past.