There are a number of cities around the world that have high-quality engineering talent in sufficient quantity, that part is easy to replicate. The complaint I consistently hear from startup founders across Europe (where I've worked) and in some parts of the US is that there is a broad and deep-seated lack of ambition or appetite to do very difficult engineering. The reasons for this are multi-faceted and complicated, so it isn't something that can be reduced to a soundbite or easily changed. The intensity of effort applied to technical problem solving that we take for granted on the west coast is very much not the default case most other places, and this is compounded by the relative lack of experience building high-performing engineering organizations.
It was really short term thinking that didn't understand the industry requirements and ended up throwing the product under a bus to get a tiny bit of upfront guaranteed income.
Most of the people I work with day to day are not just brilliant, but extremely driven as well. That was never true in the other places I’ve lived. The were lots of brilliant lazy people, and lots of super driven, less naturally gifted people.
In the Bay Area you kinda have to be both and have your eye on some bigger future, or there’s no point in being here.
Whether you'd consider that "quality of startup" or not is up to you. When it comes to hyper growth success, there are multiple structural factors that really make it easier to scale in the Bay Area, despite the 2-3x multiplier in cost per employee.
That said, feel free to skim through this (slightly outdated) list and note how a large fraction of the US-based companies are based in SF or SV: http://fortune.com/unicorns/