While support staff definitely increases with users (paid or not), beyond a certain size the number of engineering staff should be largely independent of user count. As long as you are able to run 24/7 ops, manage outages and incidents, scale appropriately, etc. the only variable should be how rapidly you need to build and maintain your software. The rest of the complexity is all handled via automation.
The big difference between WhatsApp and Dropbox is mass storage of customer data. Scaling that data for random access is orders of magnitude harder to scale than simple message throughput without storage. The fact that WhatsApp is end-to-end with no syncing also makes it's feature-set easier to implement.
Not to take anything away from WhatsApp, I'm sure they have a few lessons Dropbox could have learned from (Erlang more robust than Python at scale?), but it's really not a fair comparison.
Yep, agreed. This means that Dropbox's minimum engineering count will be larger than WhatsApp's, but I still maintain that once you have sufficient engineers to tackle the problem, it's still largely independent of user count. Or, put another way, the number of engineers you need is O(problem complexity), not O(user count).
Yes, although I would submit that in a case like Dropbox you get the VC demand for growth which means that if your product is not a natural homerun you are forced to start adding incidental complexity to try to keep the growth engine going. Then before you know it you are O(Investment Money) like Dropbox or Twitter.
Since Dropbox is making a big push into enterprise, they are hiring a ton of high touch enterprise sales people - who can't scale in the same way an engineer can.
While support staff definitely increases with users (paid or not), beyond a certain size the number of engineering staff should be largely independent of user count. As long as you are able to run 24/7 ops, manage outages and incidents, scale appropriately, etc. the only variable should be how rapidly you need to build and maintain your software. The rest of the complexity is all handled via automation.