There is nothing stopping anybody from digging into lower level languages now, in fact that is also easier than ever with open source IDEs, free compilers, fast processors, ubiquitous documentation, and helpful communities too. The mere existence of a totally open source operating system like Linux and its ability to function on commodity PCs and embedded devices is huge.
You can argue (and I believe this is the point of the article) that people don't bother going deeper because for most computing purposes interacting with very high level abstractions of really complex systems is sufficient (and indeed becoming the norm), which leaves users at a loss when asked to grok lower levels of abstractions. It's also true that there is now more complexity and there are simply more possible things to learn, making it less likely that any individual has the time to develop deep knowledge of all of the systems they use.
Those assertions may well be true, but I'd argue they are not the same thing as it being harder to learn anything in particular. It's daunting, maybe, because of the sheer possibility space, but all of the knowledge is out there and the tools are better than ever.
at some level, you're always going to be assuming the layer before reasonably works the way somebody gave it to you.
Its not cargo culting if you know where the actual dependence is, and both rails and heroku make it fairly clear what kinds of things they are doing. Even if you don't know how they're doing it, you know that without running the heroku part, you cant load the page in the browser, and without the rails part, you don't get any files you can change.
How long does it take to actually understand what all of that does? I can claim to understand it, sure--but I'm also thirty years old and I've been getting paid for this stuff for the last fifteen. (Not, like, random POKEs into memory to make syscalls, for sure, but I understood why stuff like SCREEN 13 worked, along with the general constructs of the language.) On the other hand, I pretty much fully understood how QBasic worked and its interactions with DOS at age 5. I was able to parlay that into C and C++ and into understanding how the thin virtual machine there, simultaneously into PHP and Java and how those actually worked by relating them back to lower-level concepts I'd picked up...
Cargo-cult monkeying about doesn't adequately, to me, replace understanding and insight--and "just make a Rails app and push it to Heroku" is fundamentally cargo-culting. If you don't understand how your tools work, you don't understand what you're doing. (I've written everything from CPU emulators to Rack frameworks to prove that I do understand what I'm doing.) I started doing that literally from the jump as a kid, and the systems were built so that it was something you could easily do.