fair enough but I'm fairly sure that if you traveled in time from 5y ago with a decent developer from that time he would have hard time landing a job today
Some people have an easy time programming, and the specifics - libraries, languages, etc - don't matter at all. They'll pick up that new stuff in their sleep.
I recently hired a Java guy after talking to him - he had all the right hallmarks so I was pretty sure he would be good. I gave him a task with a piece of software I am intimately familiar with. A good developer would have had to get up to gear for a week (40 hours), then code, test, work around the little kinks (there are many).
All in all an optimistic assumption of mine would be that this task would take a brand new guy a month. The dev I hired did it in less than a week!
These people are rare. They are the rockstar programmers. And if you find one, you want to hold on to them no matter what.
Team players? What if the guy can do twice as much in a week than a "team" of 5 mediocre guys?
To get back to your assertion, he then proceeded to learn Android and put a functioning app in the Google play store in less than a week.
Granted that's still Java, but the libraries are all different and developing for mobile is also different.
If I had an iOS job right now, this guy would get it, despite never having done iOS. He'd learn this in his spare time and then proceed to run circles around people who've been at it for years.
That's a rockstar programmer for you.
Greenfield development is always easier than having to work with 200K LOC codebase that is crappy for all intents and purposes. Let's see how quickly a developer can jump on, wrap his/her around everything, then make significant changes and maybe I'll believe in that nonsense.
Personally I think if a job ad includes the word rockstar, I would expect hot groupies and coke on the job (2 or 3 times a week to allow some time for actual work :)).
In mainstream programming. You don't need to time-travel to experience huge cultural and technological shifts - you can go from Prolog to Forth to Racket to Smalltalk to OCaml to Haskell and experience more of a change than a C++ programmer from 1985 would if transported to 2013.
Inside one paradigm the changes are necessarily iterative and slow. Differences across the paradigms are huge. At a given time only one or two paradigms are mainstream, and they change rarely. The same goes for hardware architectures. This makes it look like programming is stagnant, and for the most part it is. However, when the change comes - like from unstructured to structured programming or from 16 to 32 bits architectures - people who lived happily inside the main paradigm have a hard time adjusting.
I don't know when the next major shift in paradigms will come, but it will, and then the belief that the only changes in programming are superficial will prove dangerous.
The fact that Prolog isn't the same as Forth is a complete tangent.
I personally remember one and it was around the transition from 16 to 32 bit architecture (for me it was in context of WinAPI vs. MSDOS programming). That seemed like everything has changed completely and people had to put a big effort to stay relevant. The same happened - from what I hear - when OO became mainstream. The same when we largely abandoned asm for higher level languages. Basically, I'm saying that there are such 5 years periods in which the above statement holds true.
Such turning points have, I think, one thing in common - new technologies, methodologies and paradigms are not created overnight, in each case the "new" was around for quite a few years before it "suddenly" replaced the "old". It was just outside of day to day work of most programmers. That's why I think it's important to be on a constant lookout for new things in programming - or even old, but different things. One day, in a matter of months, they may become dominant and make your skills largely obsolete which will make you maintain some legacy stuff for the rest of your career. It's a hyperbole of course.
Anyway, while today and 5 years back are not that different, maybe today and five years in the future will be. And then you'll have a problem getting a job until you catch on. I'm not saying how probable it is, but it happened and may happen again. Or didn't it? What is your perception of this issue?