Forbes writer Andrew McAfee has written an article on why geeks detest the iPad, you can read it over here.
The best reason I can come up with for the over-the-top reactions to the iCosystem is that it violates important parts of the modern geek ethos. Here's my inelegant attempt to summarize this ethos without caricaturing it:
We like to hack things, to take them apart to understand how they work, recombine their elements, improve them and add new ones, some of which we've built from scratch. We hack all kinds of things--computers, cars, food, networks, governments, music and so on.
We hack some things that we don't own (like open-source software) and many things we do. Once we buy something we consider it ours to hack, and we don't need or seek anyone's permission to do so. Nobody can dictate where, how or what we hack, particularly when we're not breaking any laws...