I think this is unfair, and I'm surprised other teams are not protesting.
Mercedes, unlike Ferrari after Bahrain, used this years car from what I've heard, they've also managed to gain extra mileage, doesn't matter if it's different tyre compounds, they still got the extra mileage.
Ferrari used their 2010 car which is allowed, so that's probably why they've protested along with Red Bull.
Mercedes should be penalised, if not, then all the other teams should get to test the tyres used on their current car, which is unlikely.