My thoughts on Universal Apps:
1. An Iphone and an Ipad are two fundamentally different user interfaces. Different design interfaces needed to be treated as different products. This is my most important consideration on the topic of universal apps.
2. Different price tiers. Ipad users typically have a higher willingness to pay. By allowing user to own both an iphone and ipad version with one purchase you’re essentially missing out on capturing surplus from customers that have a higher willingness to pay.
1. You might have a good reason for using universal apps if the app is content based, such as a reference tool. If UX is not a huge differentiating factor, then maybe this is not important to you.
2. Your app is a free product, such as a social network or utility.
3. A universal version would made users happier by allowing them to get more bang for their buck. In my experience, however, the vasty majority of users won’t notice if you have an HD version listed on a separate price tier. Just look at the reviews of Rovio’s Angry Birds.