The ipad actually has half the RAM as the iphone 4, making it's processor slower. New versions will have a better screen, more RAM, cheaper storage, etc... That is always going to be the case. Holding off on buying technology because the next version will be better and a better deal doesn't always work the best. I got the ipad 3G with 64GB of memory the day it came out, mostly because I'm an apple fanboy and get all of their products. But this thing has paid for itself many times over every month I've had it just by the increased access to corporate filings. On a small easel it can act as a dedicated screen next to your desktop, just for documents. Airplane trips are orders of magnitude more productive.
The kindle is so much better for reading, but my wife stole mine and 99% of the time I'm not reading it in bright sunlight.
Also, there should be competing tablet devices running both Android and Windows out now or very soon. They will all store and display pdf's well.