I've definitely had to code up alternative front-ends routed through a server I own to access Google on slow connections. If it takes too long your browser just gives up, and the site isn't just "unusable" (slow to the point of being painful), it's actually unusable.
99th percentile is fairly arbitrary. At Google's scale, that's a $2B yearly loss in customers they could have satisfied who went elsewhere. That's roughly 200FTEs who could be dedicated to the problem more efficiently than working on their other business concerns. Is not delivering a shit website when the connections are garbage that hard of a problem?
