It's a long and fragile logic chain, but my assumption is that a lot of people got interested in technology partly out of a fascination with all the cool things it can do and partly from the conscious or unconscious hope of finding or building a system to shore up some weakness that makes our own lives more difficult.
Is Geekery compulsive curiosity?
That doesn't explain the wide variety in the available species of geek, however, or the likelihood that people who admit to geekhood in one area will go out of their way to admit equal or greater levels of geekery in other areas as well.
geekery, in that context, isn't really the result of having a need to fix things and the search for tools with which to fix them.
It's more an imbalance that pushes a person's topical interests far higher in their natural list of priorities than would be the case with non-geeks.
(Other areas of topical obsession have a similar psychological provenance but different names and behaviors. Political obsessives are called Wonks, for example. Philosophical or spiritual obsessives are Religious, "Religious," or Nutty Crunchies. Those obsessed with finance, economics and business are known as Bores.)
I know a lot of people with enough general interest in cultural anthropology to watch documentaries in which Michael Palin travels the world taunting native peoples with self-deprecating Englishisms or discussing over lunch whether the Earth really will end in 2012 as an ancient Incan calendar predicts, at least as far as they understand from a movie trailer and a photo caption they read once.
A geek has a picture of the calendar, locally cached copies of web pages with explanations of Incan calendar cycles and interviews with living Incan priests pooh-poohing the idea. (Pooh-pooh is an ancient Incan word meaning, colloquially, poop-poop.)
A real, practicing, multifaceted, category-defying geek (an actual one with whom I used to work) scoffs at the idea because, after finding an avocation as a journalism geek and a career writing about technology deeply enough to become an enthusiastic computer geek, discovered so deep an interest in pre-Columbian South American cultures that she had to go back to school to get a masters in anthropology.
Without the curriculum leading to the degree she didn't know enough about the relics, variety of tribes and cultural eras or physical science available to provide good information about those eras to satisfy her curiosity.
Going back to school to get a degree in an unrelated field is a little extreme compared to most geeks, but the impulse to dive deeply into several areas of interest is the quintessential sign of the geek.
Species of geek
There are different varieties and degrees of purity within geekendom, of course.