Googles advice is not to rely on uptime in every region.

Instead aim for uptime in a few regions, and load balance your users to regions that are healthy.

That design is far cheaper for both google and for you - and, in the typical case, users still get nice low latency to a local datacenter, and only in the rare failure case might they have to wait for latency to some other region.

They do internally. But when customers want 3 zones in Indonesia they cut corners.

Do Google host their own products on Google Cloud, or are there different sets of data centres for Search/Drive/Gmail vs Google Cloud Customers?

The recommendations are to run in multiple regions if you need this kind of redundancy. Run everything in a single region and you can be affected by an event like this.