As with anything, there are as many reasons and motivations for being drawn to QRP as there are people involved in this segment of the hobby. Just take a look at the blogs, reflectors and publications to get a sense of the variety of interests. In the QRO world there are DX'ers, ragchewers, contesters, award chasers just to name a few of the reasons hams turn on their radios. Of course some of the same motivations exist in QRP, but I don't think to the same degree.
From my observations, there are two main categories in the QRP world. There are the Builders and the Minimalist. What do I mean by these descriptions?
The Builders are those guys who actually understand how to build a circuit, tweak it, connect it to other circuits and produce a functioning radio. They speak in technical terms. They know the color codes on resistors by heart and talk about pin outs, tracings and soldering technique. These guys build radios for the sake of building it and not necessarily to operate it. They may even build the same kit multiple times. They can deal in elegant or ugly design and both styles work. These guys are the backbone of the QRP genre. Without them we wouldn't have small, efficient radio with which to enjoy our hobby.
The Minimalists are the guys who like the challenge of operating with minimal radios, they like to get everything in a single case, bag or backpack to set up a fully functional station, they like QRP for the challenge. This group will walk out of a warm, well equipped shack into the snow so they can shoot a slingshot at a tree in order to erect a wire antenna and then brave the elements to operate their radio on a battery. They might even do this after climbing a mountain. Don't be too hard on this group they probably have built a RockMite that might have even worked or they managed to get a Ramsey kit to transmit, but they will never be confused with the Builders. Three sentences into a discussion on building technique would blow their cover. These guys are radio advernturers the operators who test the designs of the Builders.
We need both of these groups to keep the hobby vibrant, it is a symbiotic relationship within the QRP world that nets out to technological advances and adventures in radio that make QRP interesting.
I suppose there are probably a few Super Radiomen out there who are comfortable in both worlds, but I would guess that, broadly speaking, most of us are one or the other.
So, what kind of QRP'er are you?