Should you maintain control over your client’s CMS?

An issue that I have come across more and more frequently recently involves content management solutions and broken websites. By broken I mean websites that are visually not as they should be. This is sometimes due to the limitations of the CMS, but more often due to the client’s lack of knowledge with regards to web programming. Now it isn’t fair to blame the client, for not everyone can be expected to be web-savvy, in fact if that was the case I’d be in more stiffer competition for employment.

So what I am asking is whether you, as a sole web developer or a large web company, should maintain control over your client’s CMS so that when something does go awry (I’ve seen the damage a missing </div> can do!) you can fix it saving the client humiliation from a broken website, or once payment has been taken for the project, should you remove yourself from it completely, and anything they do to their website is their own responsibility?

I know that more advanced CMS solutions are emerging, Cushy CMS being one, that restricts the amount of potential damage a client can do to their website, however it still doesn’t stop them from entering invalid markup. Should there be a level of understanding and responsibility between the web developer/web company and the client as to who does what, when/if the website breaks?