I suppose, if you build an app for the iPhone you don't spend a whole lot of time considering how it might look on a iPad.
It takes time and effort to add the proper UI elements for an iPad. Even adding an alternate landscape mode to the iPhone version (when there is no real case use on the iPhone itself) is wasted time and resources. That's money. The developer is only going to do that work if they believe enough people with iPads will use the app to make it worth their while. At least if they are going to do a good job of it.
Hold in mind that the iPhone emulation mode on the iPad is something Apple does, not developers. It started out so that there would be more apps for the iPad when it first launched. A stop gap that hasn't stopped. App developer's themselves are unlikely to give it a second thought. If they wanted to support the iPad, they would do it properly (one would hope) not depend on the less than ideal emulator.
So, if you want an iPad version, leave them some feedback. Maybe it will be included next year.
In the mean time I guess you can console yourself that if it were not for that emulation mode you'd have no app at all. Well, unless you also have an iPhone or iPod touch.