It's my understanding that only photos imported from a camera via the Apple Camera Connection Kit will remain at their original resolute. Photos from other sources are optimized and the sizes are reduced. I believe this is a function of the photos app and not iPhoto. The photo file optimization has been the way photos have been imported to the iPad since I've had my iPad 2, long before iPhoto was available.
iPhoto optimizes photos for sharing on social sites and in that process file size is reduced. The only way I know to export a photo from iPhoto for iOS is to tap the Share icon, the rectangle with curved arrow, and share to iTunes. Then connect your iPad to your computer, start iTunes on your computer and use the file sharing section to copy the photos back to your computer.