The parent is referring to the fact that consumer plans for nearly all ISPs don't guarantee 4 Mbps at all times. Instead they offer "up to 4 Mbps". Average performance is less than that, especially at high-usage times of day.
Historically, that's been an issue. But in fact, the FCC has been testing this, and most users' actual speeds are barely any lower than advertised (and sometimes even higher) during peak periods. From their 2014 report [1]:
"On average, during peak periods DSL-based services delivered download speeds that were 91 percent of advertised speeds, cable-based services delivered 102 percent of advertised speeds, fiber-to-the-home services delivered 113 percent of advertised speeds, and satellite delivered 138 percent of advertised speeds."
And, a majority of wired connections are advertised as "6Mbps or higher" [2] – so even if throughput at peak times was only 66% (while in fact it averages 90%+), it'd be still be plenty for HD video from Netflix, iTunes, and Amazon.
The sense of distress here is based a lot on folklore and outlier complaints. Most people are essentially getting the full headline speeds, even during peak times, and have 2+ choices for service sufficient for all but the most bleeding-edge applications.
You're forgetting the huge gulf inbetween "up to 4Mbps" and "4Mbps".