Theres a few "Universal" apps on the App Store already. Pandora and IM+ (paid) come to mind.
I think a lot of developers are going to come to the realization that many (if not close to all of us) who own both devices will not be buying two separate versions of an app. If you want my money then you need to make a universal app that works on both. Not release the iPhone/iPod touch version for 99c then expect me to pay $9.99 for the iPad version because its "HD". It's ridiculous that EA is trying to charge $14.99 for Need for Speed Shift when the game itself isn't even worth the $6.99 for the iPhone version. And to top it off, they're offering nothing in the iPad version other than higher resolution graphics. There is no reason that couldn't have been made a universal binary that would work on both with the app rendering the graphics at a higher resolution by default on the iPad. None of the assets in the game appear to have changed, it just renders natively at 1024x768 instead of 480x320. Real Racing HD offers a skinning feature, but thats not worth double the price either. Same game, same assets, just higher native rendering resolution. What a rip.
I never did buy IM+. I always used the free version. But since they're doing the RIGHT thing and releasing a universal binary that is free to existing customers, I'll most likely be picking that up.