The comparison of dogs to thermal imaging and starlight scopes isn't really addressing the picture here, it's fouled - those tools are constantly used on the public streets (helicopter chases, etc) but can not be used from the street to look inside your home because to do so would be intrusive. They actually "look" inside your home to see what is there before any suspicion or PC is developed. That is deffinately an intrusive search...
Dogs on the other hand are just detecting odors which travel from inside the building or car out into the public street. (or wherever they're working) Odor is actually microscopic particles of the substance traveling through the air. The dog's reaction to his detection of this scent is interpreted by the handler to tell where the odor is coming from. Therefore the doggy search isn't considered legally intrusive because he isn't actually sensing what is inside the area where privacy is expected - he's just sensing the odor trail that is outside (in plain view to the mutt) and following it back. (Also why a lot of those positive alerts that find nothing exist - the microscopic particles that cause odor are still there, but the dope ain't)
Correct me if I am wrong (I usually am) but a thermal imaging device actually detects the heat coming out of your house (or whatever). And the heat is just tiny microscopic particles/waves.