They were comparing it to Dropbox because that's the comparison actual users will make. Regardless of whether they want to brand as 'backup' or 'photo storage', people are starting to view those things equally and Dropbox is an EXTREMELY popular backup tool [1] [2] [3].
Dropbox even launched a feature to automatically capture photos from a device [4]. If they can't answer the 'compare to Dropbox' question well, they can't defend the business.
I suspect that the target market wouldn't compare it with Dropbox, which gets expensive if you want lots of space. They were building something for serious photographers, with one of the mentioned pain points being the time it takes to backup a photo library. I understand this — I have about half a terabyte of photos (shot in RAW) and I don't take nearly as many photos as some.
That said, Backblaze works fine for me, although the initial backup did take a while.
I don't know the pricing model they were proposing, but the "it costs $500/year for 500GB on Dropbox" line would have probably been where I started.
For me, as a photographer with around that amount needing to be backed up, I'd want to know what their service offered me over the $59/year for Carbonite (that can also back up just about anything else you want).
