Technical boss Paddy Lowe believes Mercedes' excellent development programme is one of the main reasons why their rivals haven't been able to catch up.
The Brackley-based squad started the 2014 season with six consecutive victories and many believed - or maybe hoped - it would be just a matter of time before the likes of Red Bull and Ferrari reduced the gap at the front.
Although Red Bull have managed to edge closer, Merc remains well clear of the pack and Lowe says that is down to the constant upgrades they are making to the F1 W05
"A lot of the deficit has been on the power unit side, and you wonder how much of that is fundamental and how much is short-term issues they need to learn to manage," he told Autosport.
"I would have expected more would have been short-term and been overcome.
"It's difficult to know because we're pushing in so many different areas and you don't know which areas they're pushing in.
"We've been concentrating on our own programme and we keep pushing hard to improve the car race by race - what turns out, turns out, but I'm happy we're managing to maintain a good gap."
There have also been suggestions that the only reason why Mercedes are so powerful this season is because of the engine advantage they have over the Renault and Ferrari-powered teams.
However, Lowe was quick to point out that they have an excellent car all-round.
"These cars are about system performance, not individual elements," he said.
"It's about how you put it all together. It's the power unit, the efficiency of the power unit, the aerodynamics, and the manner in which they're all put together.
"It's the collective efficiency of that package from a power, aero and suspension point of view, as well as a weight point of view.
"Our car is very quick. There are other cars running that power unit that aren't as quick, so it's a whole system."
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