Eventually the new, from scratch TCP/IP stack was done and shipped with NT 3.5 (the second version, despite the number) in late 1994. The same stack was also included with Windows 95. However, it looks like some of those Unix utilities were never rewritten. If you look at the executables, you can still see the copyright notice from the regents of the University of California (BSD is short for Berkeley Software Distrubution, Berkeley being a branch of the University of California, for some reason referred to as "Berkeley" on the East Coast and "California" on the West Coast...and "Berkeley" is one of those words that starts to look real funny if you stare at it too long - but I digress). Keep in mind there is no reason to rewrite that code. If your ftp client works fine (no comments from the peanut gallery!) then why change it? Microsoft has other fish to fry. And the software was licensed perfectly legally, since the inclusion of the copyright notice satisfied the BSD license.
All life evolves by the differential survival of replicating entities. -- Dawkins