I think it just comes down to ego with most.  If the client is willing to pay a higher labor rate to offset some of the revenue lost, and there is a contract that you are not responsible for the equipment or systems issues to do his purchases, I don't see an issue.  I would not want to go this route often but time to time I think it can work out in the end.  But it is infuriating when you design a system and the client goes and sources everything elsewhere.  It just feels like a classless way to go about things.  I understand people want to save money, but the old ways of doing things are gone and its not always an easy pill to swallow.