I have a non-aviation MBA and when I compare it to a Master's in Aviation (taken by a friend), I can see it is a totally different kettle of fish.
An MAv is aviation specific and you'll learn a heck of a lot about the industry within the course content itself. A generic MBA is applicable to any industry - an aviator enthusiast may find loads of case studies about everything from real estate groups to supermarket conglomerates but nothing about airlines (unless you pick this as your thesis, a smaller part of your degree).
All I am saying if you want to open more doors, then be prepared to take a step back to view the entire world ; but if you want to keep aviation close to your heart, then go for an MAv. For the above reasons, having a generic MBA won't deter me from considering an MAv.