There may be a unit conversion problem here, but an apartment as small as 500Sqft apartment would be exceedingly rare - that's ~46.5Sq/m.
Many cities don't even allow apartments that small...
Studios are usually around 400 sq ft.
I serve my 1200 sq ft condo with a single node, and it gets good coverage throughout the space, including the front/back patios.
My parent's 2400 sq ft house took 2 nodes in the attic + one in the back of the garage to cover the back yard.
They can hit their ISP's 150mbit/second cap from anywhere in the house or yard.
They use tablets almost exclusively and though dad still uses a laptop from time to time, he has no desire to plug it into ethernet, so a wired network wouldn't really be useful for them.
If I crunched the numbers correctly, roughly 2.5% of the US population lives in NYC alone. If you add in Boston, DC, San Francisco and other expensive cities I'd bet you can break 10% of the population in the core expensive cities alone.
80% of Americans live in an urban area.
I suspect that your biggest problem is really just your terrible ISP. I've had that problem before too, but my current one is great (and local).
Also, my phone company refuses to upgrade so I am on high-latency DSL. When a packet gets dropped in my local network, it takes a long time to get a replacement from internet based services.
You don't need high bandwidth to use the internet reliably, but you do need low packet loss, and the effects of packet loss and high latency multiply with each other -- local packet loss is much more painful if your internet is slow than if it is fast. Thus having a reliable local network helps experienced performance, even if you have a 2Mbps internet connection.