It isn't imaginary though. There's a single-sided infinity stretching out never-endingly into the future at the discontinuity where the old round ends. To wit, a Warblade and her friend could continually delay to be after the other, once each round, and eventually they might be on Initiative count -1,000,000,000 and yet they would still act before the person with Initiative count 50 in the next round. That's where the rounds start to matter. Because if you did that trick and you weren't already last at the end of the round, you'd actually start passing people until you got to last, but once you reach last and border on the infinite Initiative gap between rounds, it changes.