Why Siebel UCM uses PIP instead of Siebel Replication Manager?

Originally this was posted in one Linkedin's Siebel group that I'm subscribed, but since I got no answer, I decided to post here too... maybe a good soul can answer this one in the future because for me it still does not make any sense.

Some time ago I started wondering why Siebel UCM 8 does not uses the Siebel Replication Manager instead of using web services from PIP.

While Siebel Replication Manager can update slave-configured systems with only the absolute necessary data, PIP sends the entire "entity" (think about updating the e-mail of a contact, for example, PIP will send the whole contact in the payload).

I'm not a Siebel UCM professional, but every time I talk about it with a college I hear "it is quite the same thing than Siebel CRM, using basically the same infrastructure". I even asked Oracle support about it and all I got is:

"I contacted the Product Manager for Siebel Remote and he advised that you ask your Sales Consultant or TAM to get the answer. He is doubtful that Replication Manager can replace PIP integration."

I see no technical reason for that: Siebel CRM and UCM are products from the same vendor and use the basic infrastructure, so why would be necessary to use expensive "heavy" calls between the systems by using SOAP compared to moving tiny DX files between them? On the other hand, using PIP to integrate with other systems would make much more sense.