I imagine this could be the case for a lot of smaller tech startups, and perhaps even some larger companies that don’t have significant web traffic or ongoing real-time computer services.
Something like Gusto might be a good example. I would guess that each of their paying customers (employees of companies using them) leads to only a handful of initial or yearly setup tasks and maybe a handful of web requests per month, but represents solid revenue.
The most obvious counterexamples would be any company with persistence real-time services, like Dropbox or Mixpanel, or companies with a huge number of web requests with a very small rate of conversion to revenue, like an ad network or an ad-supported social network or media site.
Of course, the dollar amounts dropbox saved are compared to those negotiated prices.
In my experience it isn't so much the storage price itself, but the network transfer that makes AWS absurdly expensive.
Most companies don't need something like S3. They can perfectly suffice with one server, maybe using RAID-1, or just using backups. Data corruption mostly happens through logical errors anyway and nothing in S3 will protect you from that.
S3 supports object versioning, which very much will protect you from anything other than writing the wrong data for the entire history of an object.
Anyway, there's plenty of filesystems that have versioning built in as well.
Besides, I've been tasked with recovering the specific state of a database where every version of every object was available, and it was only some 200k or so records. That took me about 2 weeks. (mostly for writing code that could find a consistent version of the whole thing)
Given the storage usecase of DropBox what would be the percent of saving if DropBox indeed went with Google or Digital Ocean?
I'd argue that the core competency of Dropbox is its easy syncing. Dropbox wanted to get that to market quickly. If they had spent the time building out a data storage solution on their own, it would have meant months or years of work before they had a reliable product. Paying AWS means giving Amazon some premium, but it also means that you don't have to build out that item. It's not only about economies of scale and rapid demand. It's also about time to market.
I think it's a reasonable strategy to calculate out something along the lines of "we can pay Amazon $3N to store our data or store it ourselves for $N. However, it will take a year to build a reliable, distributed data store and we don't even know if customers want our product yet. So, let's build it on Amazon and if we get traction, we'll migrate."
S3 is a value-added service and creating your own S3 means sinking time. Even though data storage is very very near to Dropbox's core competency, it's really the syncing that was the selling point of Dropbox. To get that syncing product in front of customers as fast as possible, leveraging S3 made a lot of sense. It gave them a much faster time to market.
As time went on, they had traction, and S3 costs mounted, it made sense for them to start investing in their own data storage.
It's about figuring out what's important (the syncing is the product) and figuring out what will help you go to market fast (S3) and figuring out how to lower costs after you have traction (transitioning to in-house storage).
Yes, a lot of companies use cloud services when they don't need them. However, Google Cloud's compute pricing is reasonably similar to DigitalOcean (with sustained usage discounts) and from what I hear these companies will often negotiate discounts. AWS can seem a bit pricy compared to alternatives, but I'm guessing that Amazon offers just enough discounts to large customers that they look at the cost of running their own stuff and the cost of migration and Amazon doesn't look so bad.
Still, when you're trying to go to market, you don't want to be distracted building pieces that customers don't care about when you can rent it from Amazon for reasonable rates. You haven't even proven that someone wants your product yet and your time is better spent on delivering what the customers want rather than infrastructure that saves costs. As you mature as a company, the calculus can change and Dropbox seems to have hit that transition quite well.