This analysis is way too oversimplified. It completely ignores the shape of the traffic (real apps have peaks and valleys of usage - they don't pump exactly 100 Mbps every second of every day). Cloud providers charge the same amount regardless of how bursty your app is, and they have to provision capacity so that all customers get good performance even under unusual spikes (the more spiky your traffic, the better a deal per-MB pricing is for you). And of course it ignores all the ancillary networking HW and SW that supports these services, and all the labor you save by not having to manage that stuff yourself.

I've analyzed the cost of cloud services to death (I've worked for a couple of them) and the only way they aren't great deals is if you don't need high quality operations (i.e. if you can deal with slow-downs or occasional outages then you can do better elsewhere). Otherwise, if you're small-scale then these marginal cost differences don't matter, and if you're larger scale then call up these cloud providers and get yourself a discount off the list price.