Why doesn't a radar-equipped Tower say "radar contact"? Most/all of the control towers in my area have radar displays, and I know from visits that it shows all the same things as in TRACON miles away--even aircraft on the ground.  I hear them occasionally tell both VFR and IFR folks to reset incorrect codes, so they're clearly looking at (and presumably using) the radar display, even in VMC.

So why don't they say "radar contact" like TRACON does?  It seems a little odd that you get a squawk from Clearance Delivery, and Tower checks the literal radar contact on their screen to make sure you got it right, but then you don't hear "radar contact" until talking to Departure.

Also, some busy airports will assign squawk codes to inbound VFR aircraft coming in directly rather than via Approach, but they don't say "radar contact" then either.  This seems even weirder since in that case nobody else ever will--yet you're obviously a radar contact on their screen, otherwise what was the point of giving you the code?
From the ATC Orders 3-1-9(b)(4):


  Unless otherwise authorized, tower radar displays are intended to be
  an aid to local controllers in meeting their responsibilities to the
  aircraft operating on the runways or within the surface area. They are
  not intended to provide radar benefits to pilots except for those
  accrued through a more efficient and effective local control position.
  In addition, local controllers at nonapproach control towers must
  devote the majority of their time to visually scanning the runways and
  local area; an assurance of continued positive radar identification
  could place distracting and operationally inefficient requirements
  upon the local controller. Therefore, since the requirements of para
  5−3−1, Application, cannot be assured, the radar functions prescribed
  above are not considered to be radar services and pilots should not be
  advised of being in “radar contact.”