It's the absence of (less precise[?]) retail discs that's new and controlling.
{emphasis mine}
Why would Apple distribute any software on optical media when the drives are not standard equipment on any but one or two currently shipping computers or devices and those few will likely be sans optical drive in their next iteration?
I was at the local Apple store Sunday to get a physical hands on of the Apple Watch and while I was waiting for our appointment time I asked one of the employees how many optical drives they were selling. He replied he had not sold one in a week. No one was interested in them.
Apple has made no secret of the fact they have moved to electronic distribution of software. One of the many side benefits of that move is it enables them to narrowly target operating systems, drivers,
etc. to specific hardware configurations and thereby increase security, compatibility, and reliability. The App Store sells what is essentially a
retail version of OS X, but it is not a "universal retail" version rather a version targeted for your Mac model. I suppose they could build a universal retail version but I would not be surprised if it cost $135 as opposed to "free" for the targeted version delivered electronically.
