Sorry I'm a little late getting in on this discussion.
In business, when ownership transfers is specified in the contract or ordering document. I suspect it was specified in your contract too, and you just didn't see it.
Usually it is specified in one of 3 ways:
FOB Destination = You take title on delivery (this is the one that businesses usually try to specify -- that way if the delivery van crashes on the way to deliver the goods, it is the vendor's loss, not yours)
FOB Installed = You take title on completion of installation
The 3rd possible way is the one that business buyers try to avoid, but sellers like:
FOB Shipping Point = You own it as soon as it leaves the vendor's shipping dock. (You as a buyer try to avoid this because if it leaves their shipping dock but never arrives at your receiving dock, the loss is yours, not the vendor's, under this designation.)
"FOB" means "Free On Board" (or "Frieght on Board") which is a term originally taken from marine cargo.
I'm guessing that somewhere in the contract you signed when you bought it, you'll find one of these three designations.