It's not just one reason. That was a lure to get you to read this. But a foremost reason, in the 70's episodes, is the mood. Many episodes are somber, even melancholy. And many (or at least several) episodes end with Columbo simply bowing his head with an expression like he MUST do his job, whether he WANTS to or not. Yes he has remarked he loves his job in a few episodes, but I often get the feeling he must pursue his prey regardless the effect on his health, marriage, etc. It is his fate.

i've been lured crisp!
great post! you opened my eyes to some stuff!! yay!

there is a definite change of mood between each columbo episode. they each have their own emotion that they carry along with them. the different moods of each episode certainly puts columbo in a class of its own..(or of a very select few.
and the other thingy you said about columbo reaffirming that he is 'just doing his job', and how he humbly lowers his head...and how he has to do what he has to do....Well, that was really insightful....thanks..