Ground stations optional
Ground stations with direct line of site to satellites are not require because as described in "SpaceX adds laser links to Starlink satellites to serve Earth’s polar areas" (27-Jan-2021) https://arstechnica.com/information-technology/2021/01/spacex-adds-laser-links-to-starlink-satellites-to-serve-earths-polar-areas/ signals some of the satellites contain laser links.
Quoting from the article:
"The speed of light is faster in vacuum than in fiber, so the space lasers have exciting potential for low latency links," the Starlink team said on Reddit in response to a question about the space-laser testing. "They will also allow us to serve users where the satellites can't see a terrestrial gateway antenna—for example, over the ocean and in regions badly connected by fiber."
There is speculation that high frequency traders may seek to leverage the faster than fibre StarLink laser connections for arbitrage between different markets.