i'm with bremen.. pages is like a kid's plastic toybox word-processor. docs2go is a sturdy metal craftsman toolbox filled with professional tools. i've used docs2go for years on my iphone, picked up pages when the ipad came out and was glad when docs2go finally was updated for the ipad.
even if you only use it for viewing word (and excel) documents docs2go will give you a more faithful rendition of the original document and lose less formatting than pages, numbers and keynote do. i have experimented with dozens of technical documents. apple seems interested in only bare MS compatibility over pushing their own iWork applications. this would be great if most of the world used iWork apps on the desktop, but they don't.
as for "hidden" charges. the only thing someone could mean is the in-app store allows you to buy/upgrade from the basic version to the professional version with a one-time charge. the net price is exactly the same if you bought the pro version to begin with, it's nice they don't decide to charge you extra. while i can recommend the pro version, if you're unsure of your needs and want to save a few bucks, get the basic version and upgrade at a later time if you feel the need. you can read the product descriptions in the store to see the differences between the two.
there is no app for iOS that is going to equal full desktop versions of word, excel and powerpoint, but D2G is pretty close. the iWork apps have a long way to go.