Well, it was for me. I held off on the iPad until an iPad 3. After using an iPhone 4, when I picked up an iPad 1 or 2, I saw pixels everywhere. The main thing I use my iPad for is reading. I guessed that would be the case, so I held off on getting one until it had a high-resolution display that could display text without visible pixels.
I wouldn't say the main selling point but It's important. What do we use computers for? Reading and consuming media. Most media isn't "HD" yet but nothing is holding our written word from being rendered better.