So what you're saying is that eventually that clients will get so fed-up with using the CMS that they'll start paying you to make the updates? IMO this is a very bad plan that can easily backfire. You might soon find those clients time-and-materials all their work to a company other than yours.

The whole points of a CMS (for my clients) is to make it easy for them to make changes to their site without involving me. If the CMS is broken (and I've never used Drupal so I have no opinion of it), then it's time to use a different one.

When I used to work in the field of small software consulting, I saw a pattern repeat a few times. During the tender phase customers would place a high value on having a CMS. Repeatedly situations developed where - once they'd been live for a year and their orgtree had changed - they found the prospect of maintaining their website themselves to be cumbersome, and found it easier to send changes to us.

Only one customer was different, and they were the exact opposite. It didn't want to pay for a CMS (this is ten years ago when there weren't dozens of generic free software CMS), had little clue about how their website fitted together, wouldn't participate in designs, yet insisted on having complete control over their site. Perhaps a throw-together offering on something like drupal would have been good for them.

I've also found that those clients who want total control, often don't want to learn anything.

The time-and-materials approach makes so much more sense: Steady work for web dev firms, the work can be done by junior workers, the client gets a professional site and can focus on their business instead of messing around with HTML.