I use modules and published adventures almost exclusively. I'll modify them to fit the campaign story lines and subplots that I have running, but they stay about 70% to 80% intact.
However, concerning the post that started the thread, I don't believe modules have anything to do with the success or failure of a system. Just because I use modules exclusively, doesn't mean I have to have modules specifically written for my preferred system. I can adapt anything.
I realize that not everyone has the experience or mechanics savvy to adapt adventures from different systems, but I'd bet the lions share of DM's probably can.
It does not necessarily follow that using a lot of modules ensures the success of a system or not.
It does follow, however, that the quality of the system itself has a very large impact upon the success of a system.