As a developer for Ipad and Iphone, one of the dilemmas you are faced with is whether to sell a separate iPhone app and a separate iPad app or simply release a single universal app that works on both platforms. There are some benefits to each strategy, so it's not an easy decision. Here are my pros and cons for developing a universal app.
1: Apple encourages universal apps, so the chance of getting featured on their "Featured List" is bigger.
2: It's a lot easier to maintain one code base for a single project rather than two - especially when updating the app.
3: Customer satisfaction is increased, because customers don't have to deal with or buy multiple apps.
4: The increase in customer satisfaction could result in better reviews, translating into higher sales.
5: Services such as Leaderboards and Achievements are shared among the devices, so an iPhone player can compete against an iPad player and vice versa.
1: You cannot set individual prices for the iPhone and iPad version, since you're just releasing one app with a single price tag.
2: You can't see how your sales are split between the iPhone and iPad version.
3: App size will be bigger, because you include assets related to both versions. Apart from a longer download time, this is especially problematic if your app increases beyond the 20mb limit required to be downloadable on 3g networks.
4: You are missing out on earnings generated by people willing to buy both the iPhone version and the iPad version of the game. These lost earnings are obviously bad from a financial point of view (unless the consumer decides to provide extra positive feedback to your game as a result), but not from a customer point of view.
5: With separate apps, you potentially launch your game twice - once per platform.
This gives you two windows of great exposure (one for each platform) as opposed to one (for both platforms).
Some developers choose to release an individual iPhone version AND a slightly more expensive universal app. This eliminates some but not all of the cons listed. We chose a universal app for our game Beat the Bullies, which we have been very happy about.