Star schema?

Today we started coaching two customers (two IT people) on our data warehousing tool. They have a lot of expertise in their software and a vast knowledge of their operational domain, not to mention the intensive use of SQL, so all went quite smooth until we talked about the structure of the tables in the data mart. Or should I say... the structure of THE table (the fact table), as the dimension tables are quite simple to understand.
For a newbie it is quite a shock to see a star schema: all that redundancy... many unused columns... SO MANY columns... referring to unrelated data... Actually there are a lot of reasons behind this schema, and I shall talk about them... sooner or later ;-)