Djlawman, it is not just a thought. I once read an article where the writer concluded that the airlines are saving a lot.

Good travel agents will not knowing use these tactics, but these days there are myriad of online reservation systems where one could do so if one desires. Going back to the original question - if one does a back to back ticketing using two different airlines would that be breaking the rules?

And then there are some legal ways of saving on tickets. For example, I will often compare the fares flying out of Denver or Colorado Springs. Sometimes the flight out of COS is cheaper even though the flight from there connects through Denver.