He is a fans favourite, yes, not least because he's English and we've effectively seen him travel this recent journey with us - which is why so many are upset / bothered by it. But Aguero's won our affection without all that stuff. So you don't HAVE to 'be Mr Spokesman' or 'Mr City' to win over the fans.
I'm reluctant to suggest Joe's mouthy behind the scenes, because I genuinely have no idea if he is, or isn't, but I am minded of Ferguson's stance about very good players like Ince and Keane who the fans loved, but had just a bit too much to say too often, and thought they'd earned some right to question the manager. What we see on the pitch and the image a player creates for the media can be very different than the one behind closed doors.
Remember the Keane incident in the World Cup? some would say he was standing up for improvements in the Irish FA, but at the same time, he walked away from his teammates and left them to it when they needed him the most. Or 'Mr Chelsea' who had no qualms about shagging a former team mates ex - who knows what sort of dressing room dynamics that creates?
Again, I don't want to suggest Joe is similar to those examples, but what the fans see is a very limited glimpse.