While consumer cameras claiming 8-11 megapixels cost not much more than one or two hundred dollars, a thermal imager at a hundred times the price offers barely 0.9 megapixels!
This is because the technology behind uncooled infrared detectors (e.g. FPA microbolometers) is inherently different from the technology of visible light cameras, and also because the commercial applications of thermographic cameras does not require high pixel resolution, but rather high thermal sensitivity. That is to say, it's not how many pixels you have, but how many bits-per-pixel, in this case not of "color" but rather of degrees of millikelvin (°mk). Common sensors have a sensitivity of 100ml, or about 0.1°C
Here's some sample shots from an IRTalk thread, showing images from various sensor array sizes; even with the smallest sensor, thermal sensitivity is the key criteria -- even with relatively few pixels, the necessary information for a thermal survey is collected.
Top:Residential home with 3 different sensors.
Bottom: Outdoor substation at "high" resolution.
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