Craig Calcaterra over at Shysterball has a brief post up about why we see fewer complete games in the present than we did in the past. His thesis, and that of the gentleman to whom he links, is that because teams have more money invested in young pitchers now than they did in the past, they are more careful with their arms. They don't push their arms to their limits for fear of losing their investment entirely.
I think this is mostly true, but I want to make a finer point: it doesn't really matter how much you paid for the services of a particular pitcher. All that matters is how to extract the best value from that pitcher, or rather, from your system of training pitchers.
Once you've signed a young pitcher, the money that you have paid to him is a sunk cost. You cannot get it back. Thus, the money that you have already paid to pitchers should not factor at all into the training and usage of your pitchers. If the best way to extract performance from your pitchers is to have them all throw 300 innings immediately upon leaving high school and see which ones survive, then this will be the best way no matter how much you paid them. Thus, it would not be correct to alter your system of pitcher training and usage just because your pitchers cost you more money than they did in the past.
However, there is a cost to determining which system of pitcher training and usage is the most efficient. In the past, it is entirely possible that this cost outweighed the cost of paying young pitchers. Thus, teams simply hired as many young arms as they could, worked the hell out of them, and thus found which ones would stick. This may have been cheaper than actually determining how to maximize that value of any given set of pitchers. I think that this is highly plausible when you consider the relatively high cost of data analysis (no computers) and the relative inexpensivenesses of pitching.
Now that it costs a lot more to hire a pitcher (and a lot less to analyze data), the rewards for having an efficient system are much higher. Thus, teams are more willing to invest in research to determine which systems of pitcher training and usage are the most efficient. In the process of doing so, they have apparently determined that it is better for your pitchers to not ask them to throw twenty complete games every year.
Whether or not this is the correct conclusion is a completely different question.