Hi,
From your question i can make out your basic doubt is how can be dimension table be larger than fact tables.Few years back i had the same doubt so did some R&D and took the help of my seniors and of course google and got the conclusion.
See what happens when you delete the data from cube --It give the pop up message--Do you want to delete the contents of data target--After clicking yes--It pops up another window --Do you want to keep the data in dimension tables--if you say yes then old dimids remain in place which no longer be used with the new combination of data.
So thats how the size of dimension table gets more than fact table.
I hope my explanation gives you some insight on the same.
Regards,
AL