I kind of feel that you just read the title here. It's not talking about the 'fullest':

  An example of this would be if a music composition
  program has an easily-reached maximum song size because
  the code monkey who wrote it used a 16-bit variable
  instead of a 32-bit one. *While there are sometimes
  limitations that cannot be overcome*, the actual code
  written and the architecture used when it was written
  should have as little effect as possible on what the user
  sees and works with when using your software.

(emphasis mine)

I think it might be better rephrased as:

1) Don't add unnecessary constraints (or: Don't prioritise efficiency/etc. over the interface).

and

2) A good interface abstracts away technical problems, rather than presenting them in a different form.