no, it's not just comics, same procedure is also used in a lot's of cartoons and TV series.Interesting perspective on how comics work. Makes sense, especially if it's an untested story/market.
Take the tv-series: When the writer guild of america went to strike, a whooping amount of over 11500 writers stopped working. Lots of series had to put on hold but because the studios had some scripts on shelf they have mitigated the effect for some time. There are also other similar occurrences, lets say a studio had big problems, so they can imediately switch to another studio.
funfact: A lot of series have already produced "the last chapter", just in case something bad happened to the series.