I actually think you've touched on it a bit there. It's easier to sway somebody who doesn't have an interest in politics through bombardment than somebody who does. Loads of people who don't have a real interest in politics vote, and loads of people who don't have a real interest in politics read news papers.
I live in St Helens, a Labour safe seat. I know a large number of working class people who I would say have been directly influenced by the right wing press to vote conservative. I don't usually use anecdotal evidence but I think it's quite important in this instance. People I work with who have previously voted labour cited Miliband 'stabbing his brother in the back' as a reason to vote Con, as well as the SNP fear. I do question whether those opinions would have been formed, or cemented, without a lot if help from the right wing press.