Here's the thing about optimizing photos. This behavior of iTunes may be a little outdated but here's why I think iTunes does this.
1. Most people don't have 1TB hard drives in their computers. I think it's safe to say iTunes doesn't save the optimized files on your hard drive because it would take up more space on your hard drive. Now this probably isn't going to take up as much space as the original image, especially if the image is full 1080p or other really high resolution (the iPad can only handle up to 720p, anyway), but it can still add up fast.
2. Most people just don't have 64GB iPads. Usually, the mid-range product is purchased. This is can be the case with any product--whether that product is an iPhone, iPad, iMac, etc. The high-end product is usually the least purchased because high-end products are generally geared to extreme enthusiasts (plus, who really has the money to invest in a $5000 Mac Pro or even an $829 iPad?!). This relates to 1. because again, we're dealing with an issue of finite space on a device. Typically, people aren't going to use their mobile devices (i-Pad, Pod, Phone) just for pictures, so those files are most likely compressed to save space for other things, like music--if anybody remembers, the iPod was first a MUSIC player, yes?
3. The size of photos can vary depending on format, image ratio, color, camera, etc. but are typically between 20MB and 1MB. So, even if you only had 50 photos, you'd have about 1GB used already. Most people that complain about how Apple devices are photo enthusiasts who probably have more than 100 photos. Easily. So, you can see how quickly something like an 8GB iPhone 3G would be filled by just pictures alone?
That having been said, apparently the optimization for the iPad is better than it was for the iPhone or iPod.