!!!
I won't say that is impossible to use that much.
But Netflix -- who, if anything, is pressured to overestimate -- advises only half that speed for streaming high-definition video. [1]
Twenty dial-up modems is more than enough to make for a workable internet, outside of 3+ HD video streams, downloading disk images, etc.
And don't forget that that 10Mbps connection is likely only 512K up, so you can mostly forget about cloud backups or uploading your video for friends to see.
Side note: Everyone downloads disk images these days. Windows' quarterly update files are 3GB which will take over 41 minutes to download at 10Mbps if you do nothing else at the same time.
As far as 20 dial-up modems: I don't see where you get 20 from or even why that comparison matters. We aren't just using geocities and AIM anymore.
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.
Because it's an easy out if there are issues: it's not Netflix's fault; it's your internet.
Get to the airport three hours early; talk your accountant; have plenty of bandwidth.
It's not like someone who has <10Mbs connection and finds netflix to be crappy is going to lawyer up and sue netflix and win.