While it may be typical in your neck of the woods for the seller to split the cost of the owners policy with the buyer, I would guess it's not a requirement.  If it's not a requirement, then the seller would not be forced to buy insurance from an insurer of the buyer's choosing.  He could simply let the buyer purchase his own policy.

It makes sense that the buyer would have deference, because the buyer is the insured in the owner's policy, and also is required to purchase a lender's policy. 

In my area, the seller typically pays for the owner's policy, and the buyer pays for the lender's policy.  It is also typical that the seller chooses the title insurer, because he is paying the bill for the owner's policy.  The simultaneously issued lenders policy is a nominal cost by comparison.  However, the buyer would have the right to choose the title insurer, if he is willing to pay the entire bill.  I don't think many opt for that.