The league is changing. More teams are going to a positionless lineup. Teams are playing more small ball. And, there aren't many true centers left in the league. The league is changing their All Star ballot to reflect the changes.
No longer will we vote for 2 guards, 2 forwards and a center. This year's ballots will allow fans to vote for three undefined frontcourt players instead of having to vote for two forwards and a center. This will alleviate problems for teams like the Celtics where Kevin Garnett, who is technically a power forward is playing center. The same for San Antonio where Tim Duncan is listed as a power forward, but he also plays center.