We launched the Gmail for Mobile app in the UK, France, Italy, Germany, and Spain this week. This is a really difficult thing to do. Of course there's a lot of work in getting all the strings translated and making sure everything shows up nicely, but this is only the start.
Carriers in different countries have different devices, data plans, network restrictions, gateways, etc. It's never clear whether or not the application will run in any of the countries where you want to launch. The way things are now, the only way to know for sure is either (1) know someone in the country who has a phone and/or can buy one or (2) fly someone there. Seems crazy, but this is the only real way to know for sure.
And what if it doesn't work? How do you fix it? You could fly a developer there which is bad because (1) it's expensive (2) it's often not clear that the problem can ever be fixed (3) developers don't like having to fly all over all the time to fix very specific bugs - they like fixing more general problems or implementing cool new features. Debugging remotely is (needless to say) a nightmare. So, no matter what you do, it won't be pleasant.
I guess this is part of why mobile applications are so slow to gain popularity around the globe. Most are only popular in certain countries and are unheard of everywhere else. If it's a hassle for a company like Google, with all our resources, I can't imagine what it must be like for all the little startups.