Nest has a huge staff for what it currently sells.

I thought something similar. And then I worked there for a summer. Building hardware is much more difficult than you think, in ways that aren't immediately obvious.

Someone like Tony can easily raise capital in Silicon Valley, and Nest's products were selling extremely well across many retail locations. I'd be astonished if they were running out of money.

Why is it surprising that scaling is the issue? Tony's entire background is in devices and hardware, not large software systems.

They have a huge complex stack. Imagine building a system with tens (or hundreds) of thousands of connected nodes, all streaming realtime data that must be analyzed, and which can't ever go down. A Django app just won't cut it. And that's just the tip of the iceberg for Nest. The machine learning is surprisingly sophisticated.