Yes, in my opinion what you described is a 2-tier architecture because there is not a business layer even though the code is server-side. A business layer should contain all of your business objects and logic and your .cs pages would simply call those business objects.
I build most of my applications the same way: Asp.net front end calling SQL Server stored procedures for CRUD operations. However if I ever went to a different database platform I would have to change A LOT of code because there is not a true business layer in place. Lastly, a business layer will make your code more testable as well.
Sorry I can't help with the sister site question :)