There is not dishonor in that. The “magic” they provide is still better than the competition.

S3 and EC2 are by design commodity, low level artifacts. Like any other commodity, you should always be shopping around.

The big issue with Amazon has always been their “roach motel” philosophy where data goes in but doesn’t come out. (ie they hose you with network costs)

If you have enough scale and enough dollars, it is often cheaper to build bespoke infrastructure vs renting somebody else’s at margin.

From the perspective of a business, building your own data center only makes sense if it part of your business (like at Dropbox). Paying a margin for a service that is not part of your core model is per se not a bad thing, in most cases it makes a lot of sense. That is because if a company makes a huge investment, it makes this investment with its own capital. In theory (and that often applies to reality) a company can only invest money effectively in its core business.

This is why many companies with a lot of money still rent their offices – even if they intend to stay in the (often customized) buildings so they don't need flexibility. It just would not make sense to buy and to bind the capital in a building, it can be invested in their core business with higher returns.

An exception might be made in cases where a company has suddenly so much money that investing it all in its core business might diminish the capital/return rate, eg. through the US tax break, where a company shifts the money stored oversee back to the US. This is why for Google it might make sense to buy property, even though its not their business: They just have to much money.

Correct, but all of those are basically independent of the backend storage system. At one point you could almost consider Dropbox to be a VAR for S3 storage, with the emphasis on "Value Added."

Add that their flat rate pricing is actually a discount for moderately heavy users. If you use half or more of the 1 TB on the pro plan you’re already saving money compared to S3 pricing.[1] This is easy to do if you use something like Arq to back up your machines and take advantage of selective sync to archive rarely used files from old projects.

[1] S3 at 0.023/GB/month * 500 = $11.50

and 11.50 doesn't include traffic, which can get you even higher.