The iPad screen could scarcely be described as poor given that most people's first comment when they see one is, "Wow! The screen is gorgeous!"
It is an XGA resolution, IPS TFT LCD which is pretty much the best type of LCD you can buy. It is bright, clear and has huge viewing angles.
It is also 9.7" compared to the 3.5" iPhone 4......
I don't have an iPhone 4 but I have seen one and I use an iPhone 3G every day for the last two years. I hardly use my iPhone for reading or browsing or email any more because the extra size of the iPad screen makes it so much more useable in practice, AND so much easier on my eyes because I don't need to hold it so close. It doesn't matter that the IPhone 4 is higher ppi, you still need to hold it closer to your eyes to use it compared to an iPad, and this is what strains your eyes.
Yes the iPhone 4 screen is really nice and is great for occasional use while on the move, the iPad is the better device to use for more prolonged use if you value your eyes. Try reading a book on an iPhone for 15 minutes then look out of the window suddenly. It will make your head swim for 10 seconds as your eyes try desperately to focus again. Try the same thing with an iPad.
The iPad screen is far from poor!
Craig.