Just as an FYI for the others, Khanacademy doesn't use SQL Server. Entering to the site, I found this:
Our implementation of SQL is based off of SQLite
That's why the double quotes and text data type is used, as well as no identity definition. SQLite uses a single data type for strings which is TEXT and it has no length restrictions other than the max capacity.
I'm uncertain about the quality of the site to learn SQL. Remember that SQL is a standard with many dialects that won't follow it completely and by that reason, the dialects from SQL Server and SQLite will have differences.
On the normalization side, I guess that to teach basic queries before teaching joins, a denormalized table would be better to help the student understand what he's doing.