For me the main difference is the Op Sys. Android Honeycomb on my Galaxy 10.1. I still haven't quite got the hang of it and Apps. I don't have the prior experience with the fancy mobile phones... I do like the touchscreen :)
The Amazon free app for books is the Kindle reader (which I already have on my XP desktop pc) I have a Kindle as well.
I have to admit I am far more comfortable using a Windows Op Sys than Android, but am very slowly getting to grips with it.
I got the Galaxy Tab as iPad is tied to Apple apps - although that is supposed to be more secure as they vet them.
I am not sure about the pen drive plugging in, on my model you need to buy a separate adapter to turn the power port into a usb port.