Author here. I don't think Republicans are dumb - but I'm not convinced I'd want to invest in a company run by Bush http://edition.cnn.com/ALLPOLITICS/stories/1999/05/13/presid...
On to your main point. Sentiment analysis is still imprecise - but seeing as the majority of my (news) links go to The Guardian or Independent, and none go to tabloids - it's not a stretch to say I'm unlikey to visit a News International title.
I've never (knowingly) Tweeted or otherwise interacted with The Sun.
That's one example out of many. At one point, I was sent targetted tweets about attending a conference in the USA - I live in the UK.
If they were blindly targeted, it wouldn't feel so offensive.