I'm a C# programmer and I'm reading "Writing Add-ins for Visual Studio
.NET" (which is written in VB.NET).  I don't know VB.NET, but I can
generally read through VB.NET code and understand it, but I'm more
comfortable in C#.

First off, I generated a default VS.NET Add-In using the VB.NET Add-In
Wizard as well as another VS.NET Add-In using the C# Add-In Wizard and I
noticed some discrepancies:

1) Why does the default VB.NET Add-In code have:

<Assembly: ComVisible(True)>
<Assembly: CLSCompliant(True)>

...in the assembly, but not the C# version?  When I compile the C#
version with:
    [assembly: CLSCompliant(true)]
...in AssemblyInfo.cs, I get several errors about several extensibility
classes being non-CLS compliant (so how does the VB.NET version compile?).

2) Why does the default VB.NET Add-In have:
    Dim applicationObject As EnvDTE.DTE
yet the C# version is:
    _DTE applicationObject; (_DTE is actually EnvDTE._DTE)

3) What's the difference between EnvDTE.DTE and EnvDTE._DTE?

4) Why the discrepancy?  Why does VB.NET use EnvDTE.DTE and C# uses
EnvDTE._DTE?

Next, in my C# project, I changed applicationObject from a _DTE to
EnvDTE.DTE (to match the VB.NET code).

5) Using EnvDTE.DTE applicationObject in the C# version (as opposed to
_DTE applicationObject), why does the VB.NET version have:
    applicationObject.CommandBars.Item["Tools"]
...yet in C#, applicationObject.CommandBars does not have a member Item?
 Aren't they both using the same DLL (and are both a EnvDTE.DTE)?  If
so, how can a DLL have conditional code (#ifdef VB.NET -> expose Items
method???)

6) In a lot of the code from "Writing Add-ins for Visual Studio .NET",
there is a function called MsgBox().  The VS online help says it's in
the Microsoft.VisualBasic namespace and is within the
Microsoft.VisualBasic.dll assembly.
    A) Why isn't that dll added to the VB project's reference section?
    B) I added Microsoft.VisualBasic.dll to my C# project, yet
Microsoft.VisualBasic.MsgBox() does not exist.  Again, is there
conditional code?

I opened Microsoft.VisualBasic.dll in Reflector but MsgBox doesn't
appear within the Microsoft.VisualBasic.dll, so where is MsgBox coming
from?  I know I can just use System.Windows.Forms.MessageBox.Show() in
its place but now I'm curious (and baffled) as to where MsgBox() is
coming from.

TIA,

anon