You're missing the main point, that Columbus is considered EAST while Nashville is considered WEST. As according to time zones, as well.
Detroit and Columbus are the two teams EAST that would have a higher likelihood of entering the EASTERN Conference. They also run on EST, making scheduling a ton easier. And no, Nashville is not '500 miles closer to us'. It's maaaaaybe 250 miles further away, and by flight that's like adding another 30 minutes.
Also, you're not taking into account that we're not the only ones in our division. Raleigh, North Carolina is probably closer to Columbus, anyways. Also, the Florida Panthers sole affiliate at the moment, ECHL's Cincinnati Cyclones, would be at a great advantage to have so close to a division rival.
Divisions are loosely based on the geography back when expansion and relocation were still popular and occurring. That's not the case anymore. Here are the potential cases -
Definite:
The Atlanta Thrashers become the Winnipeg Jets and move to the Northwest Division, removing the Colorado Avalanche from said division.
Probable:
The Colorado Avalanche join the Pacific Division, removing the Dallas Stars from said division.
The Dallas Stars take the vacant spot in the Central Division, where either Detroit, Columbus, or Nashville has left.
Scenarios:
- Detroit or Columbus joins the East and into the Atlantic Division and bumping either the New York Islanders or the Philadelphia Flyers into the Southeast Division
- Nashville or Columbus joins the East and into the Southeast Division filling in the vacant slot the Thrashers left.
- The NHL removes the division name Southeast and furthermore realigns the entire Eastern Conference under new division titles potentially putting a team like the Panthers in a new Atlantic Division.
- The NHL keeps the Winnipeg Jets in the East and creates a traveling nightmare so as to avoid a new scheduling nightmare, and resolves the issue a season later.