"Because they typically introduce new technology which is somewhat incompatible with previous generations"
Just to clarify:
He doesn't meant that each year's new kit is incompatible with last year's. He just means that major generational changes introduce incompatibilities.
11-speed cassettes have been the rule for most new road bikes for quite some time now, but obviously when it was introduced it wasn't compatible with 10-speed systems.
11 has been around for a while now. Shimano has 3 "serious" tiers of road bike components: Dura Ace, Ultegra, and 105 at the "bottom". (The bottom here is the bottom of serious cycling, not the bottom of cycling generally; the lowest 105-equipped bike in Specialized's road line is $1,400 MSRP.)
When I bought a bike in late 2014, Dura Ace and Ultegra were 11-speed, but 105 was still 10. Then, for a while, everything was 11. You could (and can) mix and match within Shimano or within SRAM as long as everything was 11 speed (with the exception that you can't mix mechanical derailleurs and electronic shifters, or vice versa).
A year or two ago, SRAM introduced a new 12-speed electronic-only group at its high end ("RED"), which has since filtered down to its middle-grade ("Force"). SRAM still makes 11-speed mechanical and, I think, still makes parts for its first electronic setup ("eTap") which was 11-speed.
Shimano is behind, and still hasn't introduced a 12-speed system, but there's a lot of anticipation for it, which is what OP is referring to.
(I should also note for the record that Shimano still makes and sells lower-grade component groups, too; the cheapest road bike on the Specialized web site is intro level Allez at just $900. It comes with an 8-speed Shimano groupset called Claris, which is currently Shimano's bottom-of-the-line. They also still make a 9-speed (Sora) and a 10-speed (Tiagra).)