I saw most of the dictionaries say about the same:
from the first or elementary principles, methods, etc. to the last or most advanced; completely; thoroughly (Collins with some examples from newspapers and books)
From the most basic level to the highest level; completely: designed the house from the ground up; learned the family business from the ground up. (Heritage)
But EnglishCentral.com says the definition of the phrase is:
starting with nothing: "The young partners built a business FROM THE GROUND UP."
I feel EnglishCentral's is more accurate. Does only "up" mean "to the highest level"?