Not that I disagree completely, I'd personally love to see an sd card slot on a ipad, but there are reasons other than 'fleecing people out of money'. There's software reasons (how does the software handle the sdcard being removed / inserted. Do I provide UI to format the SD card? What data should I store on there? Should it appear as a separate storage area, or be seamlessly integrated with the rest of the storage?). There's hardware reasons (where does the slot go? Should it have a cover? Board space etc etc).
And people 'fall for it' because they want a straightforwards user experience, not one that involves plugging little fiddly things into little fiddly slots, and having to worry about how to copy all their data to their new larger sdcard (for instance). None of the nexus line of tablets have sdcard slots, for instance.
Remember that all of the internal storage of an ipad is encrypted, so even if they did have an sdcard slot you wouldn't be able to use it to transfer files. I'd love to see expandable storage on an ipad, my kids are always running out of room on theirs (although it does give me a good excuse to delete their games to make room for their schoolwork :) ).