Just to add, like all these surveys it asks for your age, sex etc (why oh why ohwhy?? Just because everyone else does?) but not where you are located in the UK ! This surely is much more indicative of any charging problems you will encounter than whether you are a 32 year old female or a grouchy 60+ bloke.
It's a good point regarding location.
General demographic data is collected as a means of understanding broadly the type of population your data is collected from.
Whilst there may be no real relationship between these and the outcome (although I think it's legitimate to account for age when discussing apps and access to technology..) it allows you to determine how generalisable the survey results are. If, for example, the survey only happens to gain responses from males, then it's perfectly understandable to caveat these findings with that fact. Same with age.
When surveying samples in order to try and understand broad issues, it's pertinent that the sample is representative of the whole, otherwise it may be biased. The only way you can know is if you ask....