Interesting development! Apple is taking "two separate platforms" approach while Microsoft and Google want to blend desktop and mobile. If you think about it makes sense. Microsoft and Google are going after a world were you pay for a cheap ARM device and it does work as desktop and mobile for you but Apple is going after customers who can pay for multiple devices.
But one thing is for sure, ARM is coming to desktop computing!
I'd take this a step further and summarize the strategy as:
Google: Blend devices so the experience is seamless, tracking across devices is unbroken, and get as much reach as possible with the free OS
MS: Blend devices so the experience is seamless, tracking across devices is unbroken, and then ultimately once people are sufficiently bought in, switch the OS to a fully subscription-based model with strong lock-in
Apple: Best experience for each unique device with strong ties between them because they make their money on the devices.
One tweak: MSFT will probably keep the OS free (and might even consider dropping licensing/royalty fees for Office & other software) but will push the Azure cloud hard onto Windows users, especially in the enterprise space
The only real difference with mobile versus desktop computing is the human interface. There are immense cost savings to be had in merging the operating systems for Apple devices if you can manage the code well enough; I'd be surprised if they don't eventually at least try to combine iOS and OSX.
Many components are shared between the two. They seem to have a single mobile OS with different variants (iOS, watchOS, tvOS). Some day OS X will be one of those variants.
Laptops are within the "desktop computers" side of the mobile/desktop split, and they have basically all the restrictions and features of phones/tablets. Desktop APIs are effectively a strict superset of mobile APIs.
I think that I agree with you now, but I wouldn't have last week. I just upgraded from the original iPad mini to a mini 4 and with dual app display, and web based IDEs like nitrous.io that run on mini 4, iPad Air 2, and the new pro iPad, and good SSH shell apps, and generally really fast operation, the iPad is starting to work for me in a limited way for writing and light weight development tasks.
I was blown away by the new Microsoft Surface Book but I don't think that I will buy one. I really like my 1080p Chromebook and along with two old Mac laptops and an older Linux laptop, I just don't see the motivation to get a new laptop. I could see myself getting the Pro iPad of a Surface 4 in the future.
I used to think that a key part of my software development workflow was sitting on my deck with a yellow notepad and a comfortable pen. I now use a tablet for thinking time.
Even if they aren't officially moving to one OS, Apple seems to be "blending" too. The past several Mac OS releases have made it behave more similarly to their mobile OS in ways that, on their own terms, made the desktop user experience worse, for example changing the default mouse scrolling direction (to make it like "dragging" on a phone) and removing the ability to show time remaining for the battery instead of percentage.
But one thing is for sure, ARM is coming to desktop computing!