It's more to do with the requirements by certain laws on keeping records for a certain period of time (usually about 3 years) in case of any illegal activity.
These apply to properly registered financial providers. Not a plain company running in a gray area with a polish bank account.
See
this.
I was just going off Mt.Gox policy as a guideline which dictates that they are obliged to do so for at least 5 years
https://mtgox.com/privacy_policyRetention of Personal Information
We will hold your Personal Information only for as long as it is necessary for us to do so, having regard to the purposes described in this Privacy Policy and our own legal and regulatory requirements. In accordance with our record keeping obligations we will retain Accounts and Personal Information for, at least a period of five years after they are closed by Members.
If Intersango are keeping information when they have no obligation to do so then they are just being awkward I suppose.