My sense is that especially internationally it's important because nobody outside of Canada has ever heard of Carleton or NPSIA. Actually most people outside of Canada haven't even heard of Ottawa or know that it's the capital. Also, Toronto (not Munk specifically) is ranked the highest in the country by employer reputation.
I'm also guessing that reputation is important in general because an LSE degree is only worth it because of the reputation, not because of the education. I mean how much can you really learn in two terms of ten weeks each? So at Munk I'm getting U of T reputation and (hopefully) a good education as well.