It's just the controller that'd need replacing, not the whole console because of added rumble.
I don't think potential buyers would delay purchasing the PS3 just because of a rumour that a new more featured controller is on the road, that they can buy cheaply anyway later.
Do you think it has affected Wii sales that there was a rumour of a rechargeable wiimote some time ago, I don't think so.
Rumour of a rumble featured SIXAXIS won't affect the PS3 sales negatievly.
it delaying me at least