floating houses

The good news today is, I finally got my 100mm lens back from Canon and it's working.
The weird thing is, I paid a big sum of money and they wouldn't tell me what they've done. The camera shop lady said that's pretty much same with all the manufacturers, they won't tell you what they've fixed or replaced. What?! Is this just a local curiosity or a common way of treating customers by Canon and other big manufacturers?