And let's be honest here: more and more developers are web/app developers.
While web developers may be more vocal and have more content on the web (this isn't unexpected, since they are web developers, after all), you shouldn't forget about the numerous other developers out there. They're working on systems software, embedded software, industrial control software, accounting and billing software, various other kinds of business software, scientific software, and so forth.
These days, these kinds of developers generally use Windows or Linux systems, running on non-Mac PC hardware of some sort. And there are a whole lot of these developers.
If you look at ARM and Microcontroller development, it's really a sad state of affairs. There isn't a single option officially ARM gives you to do Linux based application. Ironically the only software that is probably going to run on those embedded devices...Linux.
Honestly I wish they would scrap their horrible pathetic excuse for a development environment, and listen to the community who actually you know buy their devices.
Case in point. Try to compare the horridness of the Official STM32 libraries with libopencm3, which is amazing and incredibly simple.
Sincerely.. Fed up embedded developer.
Do you think? I'd be interested to see statistics on this (I'm not doubting you in saying that!). Being as web development (in my experience as a web developer and occasional software developer) is the entry level for software development, I'd have thought web developers easily make up the majority of overall software developers. Everyone is a PHP developer these days, it seems.
Perhaps you're right though (having just read your second paragraph).
edit: and to be really frank, what web developers do for a living is write software that they eventually intend to deploy on Linux.