A handful of domains will have restrictions on them, which means you can only purchase them if you meet or exceed certain criteria or have authorization (some examples are .gov, .edu and .mil). But most extensions are available to everyone. In fact, most country code Top Level Domains ccTLDs are available for anyone to purchase, even if you don't reside in the country code in question.
The one thing you didn’t discuss much in your article is how easy for the client it is, using the CMS *after* the developer walks away. One reason I love WP is I can show you how to add a new blogpost in 10m flat, regardless of your tech ability – and barring that, set up an email drop so it’s even simpler. October fits the mold of Joomla, Drupal, and a few others with a learning curve that’ll be quite a bit steeper for some clients.
Why You Shouldn't Use WordPress! And Why WordPress is Bad