Agree with t.alex for the most part but I think it all comes down to the way the apps run (similar between OS's), what apps are available (similar) and cost (similar). With the open platform that is Android it means more suppliers of HW (more types of solutions to meet more needs) and competion within this community (controlling costs).
Expected this. This is happening when there isnt any decent Android tablet in the market. With so many tablets getting released by the yearend, I guess Android market share could easily double. BTW with the new windows phone 7 OS getting released this month, there is going to be a redistribution.