String Comparison differences between .NET and T-SQL?

In a test case I've written, the string comparison doesn't appear to work the same way between SQL server / .NET CLR.

This C# code:

string lesser =  "SR2-A1-10-90";
string greater = "SR2-A1-100-10";

Debug.WriteLine(string.Compare("A","B"));
Debug.WriteLine(string.Compare(lesser, greater));

Will output:

-1
1

This SQL Server code:

declare @lesser varchar(20);
declare @greater varchar(20);

set @lesser =  'SR2-A1-10-90';
set @greater = 'SR2-A1-100-10';

IF @lesser < @greater
    SELECT 'Less Than';
ELSE
    SELECT 'Greater than';

Will output:

Less Than

Why the difference?