Is a CMS the Kiss of Death for a Programmer's Marketability?

Recently the company I work for made a decision to make a decision to choose a content management system (CMS) to use for most of our clients. In all, it sounds like a great idea for us programmers as the workload from designer to programmer would hopefully move from 30%-70% to closer to 50%-50%. But by being able to lessen our work load, do we essentially loose our marketability for the future?

According to the OECD's Economic Survey of the European Union (which for some reason included the US), the average lifespan of a job in the US is 4 years. By that measure, I have only 3 years left at my current position. So by taking a decent year to really learn a CMS and get an excellent handle on creating plugins and continuing to do so for the next two years, do I essentially loose my marketability for web development?

There's so many languages available today and each has its own plethora of CMSes and frameworks, does sitting down and picking just one or two trap a programmer into that life for the rest of his career? Hypothetically, we end up picking MODx Content Management System. It ends up being amazing easy to use (I have no idea if this is true yet.) Our turn-around time on a site goes from being about 6 weeks to 2 weeks. It has definitely been a good decision based on the "bottom-line" that the higher-ups are always talking about. Three years from now after putting most of my energy into this particular CMS, I decide that Myrtle Beach is no longer the place for me for whatever reason (I'm sick of the ocean, sick of the heat, sick of the humidity, annoyed at all the tourists, etc), and start looking for a different employer. This is when the real test comes.

Do employers look at your experience and decide for or against you based on what you've spent your last 2 years doing? I don't think I would if I was ever put in the hiring position. Employees are supposed to be investments, right? So shouldn't employers be looking for potential employees that have a great personality and thirst for knowledge and a great potential without focusing too much on past experiences? Personally I think a good programmer is a good programmer, regardless of the language they "know". You could be programming with Adobe Coldfusion for the last eight years and suddenly be looking for a job in PHP. Should that candidate simply be dismissed because he/she has no prior PHP experience? I don't believe so. If he/she programs well in Coldfusion, with a little investment into mentoring him/her, he/she can be just as good, if not better, at programming in PHP.

Now, can we expect the same sort of attitude for those of us that may end up being stuck using a single CMS for a single language? Will potential employers consider theses CMSes simply another language and put the investment in employees if they fit the team well, or will they simply be tossed into "temporary storage" until the office cleaning team comes to move them to "long-time storage" at the city dump?

With the wider, mainstream adoption of CMS and custom websites becoming more scarce, now is the time to really think about if a web firm's adoption of a CMS really is the kiss of death for a programmer's marketability.