It was no surprise that the Who kicked off Wednesday night's concert with "I Can't Explain," a song that has opened countless shows. What's harder to explain is how the venerable rock band continues to create so much excitement decades after its formation. Except for two high-level sections that were curtained off, KeyArena was packed for the final show of the first leg of the Who's current world tour, a remarkable trek for a band that hasn't had a hit in years.