There's some of that, but even rolling your own on oss software, your infra (compute, storage, network) can start to balloon really rapidly.
TBF, I think this is more of scale problem for medium to larger traffic companies than startups. I've seen this become especially acute when you're transition from a small or medium company and have started to hit those growth curves, and you get socked with these surprise bills. Something that was a tiny line item suddenly becomes... bad.
as part of engineering at sfdc, I promise you we think very deeply about backups, DR and edge cases, as well as backwards compatibility, and not breaking your code/apis.
I'd like to think we have a good track record. not perfect, of course, but don't believe everything the sales dudes say. ;o)
very minimal, extensible.