Even if an abstraction is horribly leaky, it's still useful for communication purposes. If you have 10 people on your team that speak English and one that speaks English and Hindi, then that one person will translate for the others. If you're translating a foreign concept, some foreign words might leak out, but having 95% of that translation in a form you understand makes that leakiness easier to handle.
[Aside: No one makes the argument that everyone must speak English and Hindi. But if you make the same argument that 10 developers speak C# and one speaks C# and SQL, the masses will proclaim that everyone should speak C# and SQL.]
It's the same argument when you talk about customer documentation: The document is an abstraction for the application and the code behind it, it's completely inadequate and inaccurate, but easier to deal with from the customer point of view. Oftentimes developer speak leaks out - dialog, server, xml, but it's usually tolerable, because an attempt has been made to abstract away the gritty details (i.e. Be thankful I didn't drop the source code in your lap and run).