"who, if anything, is pressured to overestimate" um, why would they be pressured to overestimate. They don't want to scare away customers who would think "well I'm not sure if my internet is fast enough..."

HD video streaming is surprisingly not the most bandwidth intensive activity. Facebook is actually more intensive. As is online gaming. And HD streaming is especially easy when its done by netflix which already has a network non-neutral setup https://www.beet.tv/2013/05/netflix-2.html. You may think "well, that 10Mbs is the same whether or not it is being streamed from next door or across the ocean", but you'd be wrong, due to the fact that low latency network connections are much more efficient at using that bandwidth.