"Sidesync allows the Galaxy Tab S to answer phone calls routed through a Samsung Galaxy S5 smartphone if both devices are on the same WiFi network."
There is an important technical difference here which is that most of the features that are now being used to tie together a constellation of Apple devices (play video from your laptop to an AppleTV, use an iPhone with a game controller to play a game on OSX, answer phone calls using your iMac, etc) operate using a network constructed on the fly, NOT the local WiFi network.
[This was true in the past for Airdrop but not most other features; but it's pretty much all the way through iOS8/OSX10]
It's not clear technically exactly how this is done --- it might be that a WiFi network is constructed on the fly, it might be through a BT network, it might be a combination [the BT 3 spec allows for using BT to set up a WiFi network which is then used for heavy duty transport] --- and the details may differ depending on the exact properties required and the HW involved.
Regardless of the tech details, the Apple solution provides a superior user experience because it allows your "personal network" to move with you and to work without having to validate. eg your phone should still just talk to your laptop in a hotel room, even if you have not paid for hotel WiFi; or you should be able to go to a mutual friend's house and stream a movie from your phone to their Apple TV without having to connect your phone to the mutual friend's network. (I say mutual friend --- someone you're unlikely to visit again --- because, sure, a friend you'll probably connect your phone to the WiFi network for other reasons since you'll frequently be over.)
Now that Samsung knows the direction they want to copy, it's not clear to me if they can, at least not right away. Depending on the exact HW involved, it may take another refresh round for all their various pieces (phones, tablets, Galaxy Gear, their inevitable equivalent to ChromeCast, etc) to get good enough BT/WiFi HW. There may also be a problem with APIs. Done incorrectly this sort of ad hoc networking is obviously a security disaster waiting to happen --- you don't want random phones walking by to be able to connect to your laptop --- and it's possible (I don't know the details) that most of Apple's work has actually been not in getting the HW to work but in the OS and APIs to get everything to work SECURELY. Airdrop (which has more user intervention) may, in fact, have been a deliberate prototype for the whole system --- a test case that could have been shut down fairly easily if it was discovered that there was some overlooked conceptual security flaw.
While one can probably trust Google to get the upper layers correct when they get around to copying his, you're a braver man than I am if you're going to trust Samsung's legendary attention to detail and concern with providing timely updates to this sort of aggressively new security environment.
