How exactly would they stop themselves from being listed on Google? A right to be forgotten request? Their decision was to ditch Google Analytics, not to disappear from the web.
Robots.txt. I think it's interesting that you say that removing yourself from Google is the same as "disappearing from the web" implying that the web is Google. It's not. Perhaps they should use alternative forms of outreach, something I am considering with my company.
Google is not the web, you are correct; but for all intents and purposes, it's the web's phonebook. You remove yourself from the phonebook, you make it very difficult for people to find you, or your business.
There are other ways to promote a business outside of search engines. The point is you can't say you have "ditched Google" while still being part of their systems that collect user data.
For a less obnoxious answer: if users choose to use Google, it's not Spideroak's problem. By dropping GA, they're no longer forcing users to be subject to Google's tracking.
