The crux of this study is assuming that other life forms need an environment almost exactly like our to thrive.  Here is a bit more on their study:

More heat than light
Unlike traditional SETI surveys, Wright and his team did not seek messages from the stars. Instead, they looked for the thermodynamic consequences of galactic-scale colonization, based on an idea put forth in 1960 by the physicist Freeman Dyson. Dyson postulated that a growing technological culture would ultimately be limited by access to energy, and that advanced, energy-hungry civilizations would be driven to harvest all the available light from their stars. To do that, they might dismantle a planet or two as feedstock for building star-enveloping swarms of solar collectors. A star’s light would fade as it was encased in such a “Dyson sphere,” but Dyson noted the constructions could be detected by the mid-infrared glow of their radiated waste heat—essentially the same phenomenon that causes your computer to warm up when it’s running. In 1963 the Russian astronomer Nikolai Kardashev extended these ideas by developing a tripartite classification system for a civilization’s energy use. A “type 1” civilization would harness all the energy of its home planet whereas a type 2 uses all the energy of its star, perhaps by building a Dyson sphere around it. A type 3 civilization would be capable of using all the energy of its galaxy, presumably by encasing all its stars in Dyson spheres.

What do you think?  Does this sound reasonable or is their study flawed?  You can read more from the link below to Scientific American.  What if there are life forms based on other environmental factors?  If you look even in our own oceans there are simple life forms that thrive in sulfuric environments with hot temperatures.  Whatever your opinion is this subject is interesting and likely will be debated for a long time.

thank to Lee Billings and Scientific American for the great write-up