I think you should know all the SCMs you can and be able to switch between them.
Sometimes I feel like the modern programmer is expected to spend more time learning to use multiple implementations of the same basic concept, than on actual programming.
'tis true though. Imagine how many companies out there looking for specific programming skills:
1) RoR NINJA!
2) jQuery EXPERTS!
3) JSF and/or Spring _and_ Struts2
4) C#, ASP.NET
5) All-things XML (XSLT, XSL-FO, XQuery, Xwhatever)
6) Specifically asking for DB2 or Oracle (not DBA, but for a typical developer position)
Instead of the fundamental programming skills like fundamental Data Structure and Algorithm, fundamental RDBMS, fundamental Software Engineering, etc.
On the other hand, I think Zed is just trying to be sarcastic to those who said that "you must keep on learning new things, like myself, see... I'm learning GIT" when it first came out but flat-out refused learning other things at the same time.
I took a job hiring a RoR ninja and jQuery expert as lead dev (for an alpha app) and immediately rewrote it in Django and MooTools/Google Closure. You can know the trendy stuff but still develop with solid software, provided you have some latitude in technology decisions.
Sometimes I feel like the modern programmer is expected to spend more time learning to use multiple implementations of the same basic concept, than on actual programming.