If you've bought [App X] for the iPhone and the developer makes [App X] for the iPad, should you get the iPad version for free?
We've seen developers like Instapaper's Marco Arment specifically making "universal binaries" so users who bought the $4.99 Pro version can download an iPhone update, install it on their iPad, and get an iPad-specific user interface (UI) as well. (Think of it as two similar apps in one handy download).
We've also seen leaked screenshots have shown "HD" or "for iPad" versions of many popular iPhone apps and games that are being released as separate, all new downloads. In many cases these HD apps offer substantial differences brought about by the bigger screen real-estate and beefier processing power of the iPad and will carry their own price tag and perhaps be more expensive than the iPhone versions due to the greater effort put into them (more pixels, more functionality).
Some users no doubt feel entitled to free iPad versions if they already bought the iPhone version while some developers likewise feel entitled to get paid for the work they put into making different versions for a different device.