Plugin not pushing updates

Greetings,
I just finished my first plugin and I have it in the plugins area: http://ww.wp.xz.cn/extend/plugins/foxypress/
For some reason, I have made two updates to the repository and they come through on that page just fine, however, within wordpress, I never receive an alert that an update is necessary. Am I missing code in my plugin to inform my users in the dashboard that they need to update? I’m confused, but I thought I read that wordpress automatically pushes updates every 15 minutes. Any help would be appreciated. Sorry but I’ve been searching all day and haven’t found any answers to this question.
Thanks,
Adam