Well, you have 80,000 available tickets over four shows vs 120,000 tickets over two shows. Actually they played Toronto 3 times on 360 so that is 180,000 tickets vs the 80,000 they played to on Vertigo.
No matter how you stack it, people are getting locked out of the show when you only make 80,000 tickets available when your capable of playing to 180,000.
Plus with multiple arena shows, die hards go to multiple shows, perhaps all four shows, which is another factor which displaces and locks casual fans out of arena shows. No, not everyone, but still a significant number.