Who employ these CMS?
If you think that these CMS are available free-of-cost and used only by those who can’t afford to spend too much on web development then look at the list of the legendary industry giants. The industry leaders include audi.com, twitter.com, official websites of Cisco, Brazilian government, Sony, BBC etc are based on open source CMS.
Most of the educational sites and tutorial blogs like cplusplus.com, w3chools.com, freeonlineprogrammingtutorials.com, killerphptutorials.com are also grounded on open source content management system. So, open source is indeed the way to go, unless you’re really looking for something out of the lot.