Hi Sheila, I went to "The Local.ch" and indeed the survey popped up after a few seconds. I completed most of it, but got fed up almost at the end and exited it. It is pretty clearly intended to get a survey of readers, starting by forming a demographic picture of those answering the survey and then get information from us as to what content we like, what we would like to see more of, etc.
The question on your income, expressed in brackets, was the 8th (h) question, and the survey goes on with many more questions. In fact, I doubt that you can really complete it in 5 minutes, as they claim at the beginning.
I think you did right to shut it down if the question regarding your income bothered you. Whether it was because you disagree on its relevance, or because of privacy concerns: you replied to it anonimously, of course, but I am sure a cookie was placed on your browser, so that future ad content that pops up may reflect the profile they built on you.
So, the reason for their trying to get that information from you is either to tailor the ads you will see, fitting them to your socio-economic consumer profile, or else to analyze and filter the results of the survey for, again, lucrative purposes. Probably for both reasons. In the latter case, that means that they will listen to the content suggestions and preferences of those with a higher income, as they constitute the preferred market for their advertisers.
So, given the nature of the survey, I would think in this case it was a relevant question, but I think there are legitimate reasons for you to refuse to provide the information.
Hope this helps.