1. Doing some experiments on the marketing side, especially keywords, before launching everywhere. The first week/month on the app store gives a boost to keyword rankings that can be leveraged to build good traction. Unfortunately it also requires some experimenting to get them right, so this initial launch in 1-2 countries can provide that data.
2. Building some traction and credibility so that when we launch on the other app stores, we can build on that (for e.g. #1 on the Canadian App store would have a nice charm to it, if we achieve it!). This again helps with point 1 (better traction in launch week/month).
3. Ensuring Support is not overwhelmed by unforeseen issues. We have tested a lot, but never know what kind of crashes or even minor bugs might be seen in the wild. We want to be awesome at customer experience.
4. Gathering feedback in general.