Re: Why to use SAP PI for integration between SAP SRM 7.02 and SAP ERP 6.0?

PI is not mandatory for Central Contract replication to ERP. You can still use Idocs (BLAORD & BLAREL) for integration.

If you plan to use webservices for new features like service hierarchies etc. please refer

http://scn.sap.com/community/pi-and-soa-middleware/blog/2012/06/13/transfer-of-central-contract-from-srm-to-ecc-using-web-services-without-pi