No doubt the surveys are sold on to those companies who want consumer information from the target respondents on future buying intentions.
As in the current poll. If a large proportion say there limit is £750. Then you may find that the advertisements running down the side of the web page will target laptops in that range.
They will also give interesting information to those who just buy the magazine and don't visit the website.
It is just recently that the don't know and sometimes none of the above have been added to the polls.