For Dropbox, it is their core business. For Google, it's a drop in their massive bucket of cash that comes from advertising. If business reliability matters to you, Dropbox seems comparatively better.
I dont think it is fair to equate the fact that Google Drive is less reliable than Dropbox, just based on the fact that Google has more irons in the fire compared to Dropbox. They also have orders of magnitude more employees and resources than Dropbox.
I think there are two kinds of "reliability" getting conflated here. There's reliability as in "this is built on the stable foundation of a big system and has a bunch of engineers ensuring it's Highly Available" -- both Google and Dropbox can give you that. Then there's reliability as in "this product won't blow away in the corporate-political wind" -- and Dropbox is the only one who can truly say that. (Though Google Drive is pretty core to a lot of stuff Google does, e.g. Android, so it's probably not going anywhere either.)
On the other hand, Dropbox is a one-trick pony, providing a service that is easily replicable and becoming increasingly commoditized.
Dropbox don't even own the hardware they store your files on.
Google own the data centre, the hardware, in many cases the device (Android devices, Chromebooks, Chromecast, Google TV etc.) you use to access their services, and increasingly (with Google Fiber) the connection between you and them.
It sounds more like cost-plus pricing rather than value-based pricing. At the same time, it makes sense for Dropbox to go on the higher end of the pricing spectrum and drop it if things don't go as well as hoped since it's much easier to drop price than ever to raise.
If you're comparing Drive to the Reader fiasco, keep in mind that Drive for business is a paid offering.