This is a great article from Michael Gray over at Graywolf: How Often Should You Update Your Website.
I encourage you to read the whole article.
In particular I love this quote:
At this stage, most websites really should be running some sort of CMS, WordPress, joomala, drupal, pixelsilk or something else … the downsides to using a CMS include things like maintenance and updates, which in some cases come so frequently they can become burdensome (look squarely in the direction of WordPress and Matt Mullenwegg).
WordPress now powers over 14% of the world’s top million websites, but as many people are discovering keeping a CMS driven website (whether it is WordPress, Drupal or Joomla) up to date isn’t trivial. When people first launch a CMS site they don’t necessarily realise what is involved.
At OM4 we develop client websites that often carry a design put together by a graphic designer using Photoshop or Illustrator. Normally this would mean a client now has a custom WordPress theme that *they* need to keep up to date. Well, at OM4 we host the sites we build, support them AND keep them up to date with WordPress and WordPress plugin updates.
Most of our clients don’t realise how important this is (they are too busy running their business), but over time I hope more and more people will see the value in this service.