Earlier quoted context omitted.
In the Googleplex they have networks designed to be slow and crappy to test exactly this. All people working on consumer facing apps and sites are encouraged to use these crappy networks on a day to day basis.
I wish there was more evidence that they used them. Far too often their software seems to assume a superb connection. Personal "favourite" is their Newsstand - it will ditch cached stories whilst out and about because it briefly got a connection on the Underground, only for the content to not download (precisely because you're on flakey Tube WiFi) and boom the best use case for that software is ruined!
I had a nearly seamless (albeit slightly slower) experience browsing Instagram on that slow connection despite the fact that all of the content was photo/video media, so I know the connection was not completely useless. It seems that Google engineers can't even fathom the possibility that someone would have a slow enough connection that a 5MB file might need more than a minute to download. This is frustrating.