I wouldn't agree with this. I think it is just a coincidence that the good C# people you know struggle with basic SQL stuff.
I often get the most basic questions SQL related from VB.Net and that is another coincidence.
IMHO being a C#/VB or any other .Net language developer is irrelevant to one's knowlege with SQ server as well.
I said that those were my observations. Yes, it could just be a coincidence. Yes, I've seen very basic SQL questions from VB.NET people....just not as many.
However, I also believe there's a chance that a slighly higher % of C# people have been in environments where others wrote database code, whereas a VB.NET person might have been a tad more likely to write database code himself/herself.
(Part of the reason I made the observation was "in fairness"...there are many trends that favor C#, so I wanted to throw one in from the "other side", and that's probably the biggest thing I've noticed).