Thanks to all who have responded and for the range of interesting answers the majority of which are that exposure and development are of equal importance.
The motivation behind the question is that the experiment that I mentioned in my original post involved developing 6 different films in the same developer. On my travels I make many photographs, mainly 35mm, for no other reason than I love to make them. I always give full exposure no matter what format I use, working on the basis that if it is not on the negative it cannot be printed, a point that has been made in posts in this thread. I have always been a believer in exposing for the shadows and developing for the highlights, consequently I always check the contrast range I have to deal with.
The experiment I mentioned happened because I had 6 odd rolls of film that were of little importance so instead of loading and developing them seperately I was lazy and processed them all together in one tank. The films in question were FP4, TriX at 200 and 400 ISO, Neopan 400, HP5 and Tmax 400. The developer used was Fotospeed FD30 1 to 9 for 6 minutes. The interesting end result was that Tmax was the only film that failed, the negatives were extremely under developed but the other 5 rolls produced very printable negatives. The TriX rated 200 ISO was somehat more dense than I like but still printed well.
As a result of this experiment I reached the conclusion that exposure was the most important. I hasten to add that I do not advocate sloppy developement techniques.