A big topic when Mike Tomlin took over as Steelers coach three seasons ago was whether or not he would switch the defense from a 3-4 unit to his specialty, a 4-3. He dispelled those thoughts by retaining Dick LeBeau as defensive coordinator and keeping the 3-4. It was the right decision — and helped him win a Super Bowl — because most of the talent on the Steelers’ defensive line and at linebacker was best suited for a 3-4. However, the 4-3 talk could heat up again by the end of the season, especially with the news Wednesday that defensive end Aaron Smith will be lost for the season with a shoulder injury. For a 3-4 to be effective, a team needs special players at key positions. Smith is the perfect end for a 3-4 because he’s tall, powerful, unselfish and can hold up blockers to free up other guys to make plays. But he’ll be 34 next season coming off the shoulder injury and most likely won’t be as effective in that rol.