Adding zwave support was great by UDI. It protects them and us should something happen to Insteon although I really don't see that happening. It also allows us to fill in with devices where Insteon might be lacking or vice versa.
Insteon is trying to grow the European market along with quality improvements, and new devices to satisfy their biggest customer (us -US market). Keep in mind, the Insteon catalog was not where it is now when it first started. In time, you will see more growth in other areas. They do not have a google budget. They are limited to where they can spend their dollars. Once the European market grows more, you will see more devices marketed for them.
The open nature of Zwave does have benefits of more choice and protection. However it also means more headaches too. Not every zwave device works with each other. You can run into compatibility issues with some things. Generally with insteon and the ISY this is not the issue.