As is the fact that you have to migrate the data from non-Google servers -- either your own or some other cloud provider -- to qualify, since you're going to pay for the sending the data, junk or otherwise, you are dumping into it.
Cold storage is absolutely a necessity when you reach the scale of imgur, unless you want to run the service incredibly inefficiently.
imgur keeps photos forever [0]. To do so without some kind of cold storage infrastructure in place for all the millions of photos that will probably never be seen again, or perhaps at a rate of once per year, would be infrastructure cost suicide.
Facebook faces a similar challenge and has gone in to detail about how it developed a cold storage strategy to deal with it[1].
I would say that for a service like imgur there is probably a level of parity between the amount of importance they need to place on content delivery and on cold storage.
[0] https://help.imgur.com/hc/en-us/articles/201476457-How-long-...
[1] https://code.facebook.com/posts/1433093613662262/-under-the-...