I have worked for either established and startup companies (admittedly with varying success). I think it has more to do with the composition of the team. As engineers there are a lot of different experiences we can bring to the table, but some of us have had the transformative experience of being on projects where the testing was right, in how to do and the amount, and we have seen how it helps us on a daily basis to move faster and be humbled by the bugs that we'd otherwise have released, or that we'd otherwise would've had to troubleshoot on a remote system rather than fixing them minutes after creating them. I'm now making it a point to expose my team members to the same awesome experience. But I also understand that, as you're building a startup team, and there are many things you have to get right, this may be a skill you would go without.

Also, I'm not advocating 99+% test coverage for new (startup) projects, but one could start with some tests selectively for core functionality or the most complex parts, and already enjoy a great overall benefit.