I never quite know what the dictionary definition of a blog actually is but I'd certainly advocate some kind of 'Latest News' or 'Articles' section that has pages added regularly talking about your company news or latest projects/clients or some industry relevant stuff.
If you check my bro's site at;
Computer Repair Bristol | Bristol Computer Fix and look down the left hand side you can see our efforts at it. This is the site we probably stay on top of more than the others. As Paul says, it is hard work!
The reason for having an area of your site that gets added to regularly is that Search Engines love fresh content and recently and regularly updated websites. If you just have five pages with your services that never change you'll struggle to get noticed.
As Paul also mentioned, the good thing about a CMS is that things like your sitemap should get updated automagically with your new page references and so makes sure that Search Engines find and crawl your new content when it is live. Tweeting, Digging and Liking your new pages is also a good idea.
I do indeed advocate ModX but that is because I like to code a layout from scratch. From a code novice's point of view, Wordpress is more immediately satisfying because you can plug in a template and off you go. If you want a bespoke design or one that fits exactly to your current website then I find hacking a Wordpress layout is time consuming and takes some decent knowledge of how the WP templating system works.
I'm not adversed to messing with templates as I use Prestashop for e-comm and that uses the 'smarty' templating system which is a whole other ball game. But, for a simple website, the freedom to code whatever I like and then 'plug in' the functionality I need wins hands down for me every time.