Inventory Manager shows the current price of the item, and the #1 vendor *not* necessarily the current vendor.
It’s currently not designed to show any preference, just simply the #1 vendor. Some users may want the cheapest, other’s the primary, and yet others the last purchased vendor.
Inventory Manager is designed as simply a listing of information, not as an ordering guide.
The Shopping Cart vendor assignment takes your preference into consideration when it assigns vendors (i.e., cheapest or primary). That’s where the ‘intelligence’ is built in. Please see the Help on that option (Inventory > Orders > Shopping Cart).