I have heard that there is a very large amount of commercially sold software that is written in Visual Basic.
At one time, I would consider that statement to be true, but nowadays I am not so sure its that great a percentage. Then again, I haven't used VB, let alone BASIC, for anything serious in several years, so I don't know what the truth is.
I do know a lot of people use the .NET languages, and from what I have seen VB.NET is "BASIC" in name only; it actually seems like a mashup between C, VB, Pascal, and Java - I think it might be an artifact of the fact that all .NET languages share a common runtime or something like that, and it reflects in the languages for some reason. I can barely tell the difference between a piece of C# code and VB.NET code, what little I have seen. I think a lot of VB developers have likely moved on to C# (once again, pure speculation on my part).
I don't really worry about all of this any more; the majority of my work both professional and personal are done using open-source (or standardized) programming and scripting languages on *nix OS platforms...