What app? How well known is it? What is your competition on both platforms? Have you marketed the Android version as much as the iOS version?
Findability within the Market might also be a factor. A search for "swedish" in the App Store, and it's on the first screen. But it's quite a long scroll down on the Android Market.
I'm sure some people find apps from within the store (e.g. searching for "swedish") - but I expect most to come from youtube (where there are lots of GoSwedish videos) and then search for the app by name.
Update: Or maybe I just need to do more to get the word out. I sold 10 Android copies yesterday! (Thanks HN!)