Is there a difference between MEA and MOCA within 22 nm of a VOR?
You are right. Within 22 nautical miles of the VOR, there is no practical difference between an MEA and a MOCA.

However, it should be noted that the 22 nmi is only a limitation if navigating via VOR's.

14 CFR - CHAPTER I § 91.177  Minimum altitudes for IFR operations


  (a) Operation of aircraft at minimum altitudes.
  Except when necessary for
  takeoff or landing, or unless otherwise
  authorized by the FAA, no person may
  operate an aircraft under IFR below—
  
  (1) The applicable minimum altitudes
  prescribed in parts 95 and 97 of this
  chapter. However, if both a MEA and a
  MOCA are prescribed for a particular
  route or route segment, a person may
  operate an aircraft below the MEA
  down to, but not below, the MOCA, provided
  the applicable navigation signals
  are available. For aircraft using VOR
  for navigation, this applies only when
  the aircraft is within 22 nautical miles
  of that VOR (based on the reasonable
  estimate by the pilot operating the aircraft
  of that distance)


The MOCA provides "obstacle clearance requirements for the entire route segment," so if the applicable navigation signal is GPS, and you're receiving it, then you've met the requirements. This is why sometimes you see a MOCA on segments which aren't within 22 nmi of any VOR.

One other practical difference to keep in mind is that, especially in mountainous areas, you're much more likely to get radar coverage, and have better communcations clarity, at the MEA than the MOCA (I saw this a lot in Idaho). In those cases, ATC is probably going to prefer the MEA.