It is really not that hard to tell if an app is written for the iPad; though a bit of experience helps.
If you do a search, the iPad apps clearly show up in the iPad section. Universal apps will show up under both.
If there is a plus mark in the price button, the app is universal, and will display well on both the iPad and iPhone/iPod Touch.
You have to interpret a bit when reading the requirements in the app's description. If it only mentions the iPad, then it is an iPad app. If it mentions the other devices but does not have a plus mark in the price button, then it will work on the iPad, but only in the emulation mode you've already discovered.
Another indication that the app is for the iPad are the screen shots. If they show only iPad shots, the app is probably iPad only. If it only shows iPhone shotes, it will probably only run in emulation mode. If it shows both, it's universal. This is also where you'll get clues as to whether the developer went to the trouble to create a true iPad user interface, or just blew up the iPhone's.
Out of the more than 500,000 apps in the apps store only about 15,000 are written for the iPad. (last stats I remember reading) That's still massively more tablet apps than any other store can brag about; and I've noticed that best developers are well represented among those 15,000 apps.