Let's be honest, that's no suprise. A team like RBR isn't going to contract a slow driver. And neither are Ferrari or any other top team. But I suppose that Vettel would have more fans if he wasn't contracted by an "upstart" like RBR, but by a more "prestigious" team. Ferrari, McLaren, you get the idea.
It's hard to tell which cars is the fastest and what's down to the driver's ability. All I know for sure is that Vettel posted very impressive results back when he was in Formel BMW, where everyone did drive the very same car. He also did perform well while he was with Torro Rosso. And back then, he seriously wasn't carried by his car.
Everybody loves an underdog.
A lot of people loved Schumacher when he was battling against a superior Williams. Fast forward 7-8 years and he was widely hated because he always dominated. This is the same problem with Vettel.
It doesn't really matter what team he's a part of. The car performance is what matters. Vettel has had the fastest car for most of the past 4 years (Except the beginnings of 2009 and 2012). Vettel was the underdog in the slower car in 2008 and the early part of 2009. His fanbase grew rapidly as people began to appreciate his talent when in a not so competitive car. But as he won two consecutive world championships in the fastest car, people have started to despise him.
Yes, he hasn't had the fastest car for all of this year, but on average they have only been slower than Hamilton's Mclaren which is much more prone to reliability issues (Like the 2009 and 2010 RBR). So in other words, he's had the best package overall underneath him.
In contrast to Vettel, support for Alonso has improved massively since his popularity low in 2007. People say it's because he has matured but I kind of disagree, I feel there is more to it. Now I never did like Alonso when he was with Renault or Mclaren, but the past few years at Ferrari he has shown that he is one of the best, if not the best driver on the grid. He's done this in a car that has never been quite as good as the Red Bull or the Mclaren, except for the odd race (Hockenheim 2010 comes to mind).
I can guarantee that had Alonso been in the fastest car and winning those championships, he would be as much despised as Vettel. Likewise, had Vettel been in the Ferrari and finishing 2nd or 3rd in the championship each season, he would be more of a fan favourite today. When a driver is winning, people love to hate them. Not all F1 fans like predictable racing, even if it's their favourite driver at the helm.
I'm not a fan of Vettel, but earlier this season I saw some of the best racing in the F1 field from him. I thought he was driving beyond the car, particularly his performance in Spain. I know he's a good driver, one of the best infact. But when he gets into that Red Bull and blitzes the field I really hate him. He needs a bit of ballast to even the field out, because watching him dominate for several consecutive races is really boring (Thank god his streak was broken in Abu Dhabi). At the start of this year things were looking good. There was 6-7 teams capable of taking a win. Mclaren looked to be the fastest but only on certain track layouts. Since Singapore though, Vettel has had the car underneath him to dominate once again. What looked to be one of the most exciting championships in recent years has come down to Vettel leading the championship for the final race, in the fastest car. I doubt even Alonso can snatch it from him at this point; it's pretty much a foregone conclusion so long as Vettel finishes the race.