McLaren are probably also in that category due to their long track record and unchanged engines. That'll come asunder in 2014.
Although if McLaren continue to be the only team putting the Mercedes brand on the top step then Merc will do all they can to keep them there in order to bump Renault and Ferrari down.
Yes, having a works engine supply is a huge advantage to the Mercedes team, but the downside is that it boosts expectation. Failing to capitalise on that advantage is an easy target in criticising their under performance.