That's a limitation of many PDF readers on the iPad. They don't support interactivity well. There are a few that do. Here's a posting on InDesignSecrets.com that I did on the subject of differences between PDF readers:
My favorite is PDF Expert. However, I later found I had to outline the type if I used them in an InDesign-created button.
Thanks for the response!
Looks like I need to go into Acrobat itself to change the individual button settings for the ones that does not work on the ipad. They seem to work after I change it to 'Go to page view' instead of the command from InDesign.
That's because the ones in InDesign use the Execute Menu Item command, but the iPad doesn't have menus in the reader apps. Go to Page View gets around that.