Yes, Z-Wave as as protocol is basically synonymous with a Silicon Labs product line, to the degree that the different versions of the Z-wave standard are more often referred to by their Silicon Labs part numbers (500 series, 700 series). This does seem to hold up the price of Z-wave products but, to be fair, they end up still being pretty competitive with a lot of other options, although usually more expensive than the most cost-optimized WiFi products like Tuya devices.

And at least for a long time held back the quality of open source solutions. There was (is?) frustration in the developer community in not having access to the Zwave spec and documentation.