Hi Kyle.
This is a feature by Apple Appstore, which gives Ipad users a larger variety of apps to choose from.. It could possibly sell more of your apps too ?
I do not believe its possible to exclude your Iphone app from Ipad installment. Your best option would be to generate an app specific for Ipad. You only need to resize your graphic, and control the alignment of your elements.
Correct me if im wrong.