Ha... I just went to purchase Twitterific from the Mac App Store in Canada, and the price is $27.99. Sorry... that's a deal-breaker for me.
The current exchange rate would only be $24.97, so to be charging an extra $4, when there's zero extra cost to the development team, doesn't sit right with me. I will not purchasing it simply out of principle.
The company isn't choosing to charge more in Canada; the company just sets the US price, and then pricing in other countries is automatically set based on the last batch of exchange rate (or whatever combination of adjustments) based pricing that Apple determines and enforces.
So it's not a case of Iconfactory deciding that Canadian users should be charged anything extra.
(Side note, $27.99 - $24.97 is $3.02, not $4. But I still understand your point. Try taking it up with Apple, though, not Iconfactory.)