If it's ready for the Olympics (big if), the cablecar will be a convenient additional transport option between two major Games venues. Even if it's not ready for the Olympics, the cablecar will be a popular tourist attraction. Whether it's ready for the Olympics or not, the cablecar will provide additional cross-river resilience if ever the Jubilee line or Blackwall Tunnel are closed. Whenever it's ready, the cablecar will be bugger all use for commuters, saving incredibly few of them very little time.
Two million passengers a year? That isn't much. It's only 5500 passengers a day - the equivalent of two hours peak-time capacity. It seems that nobody expects this cablecar to be packed, nor even busy. That'll be because it goes from not-quite The O2 to not-quite the Excel exhibition centre, which isn't a journey 99.99% of London's population ever needs to make. For comparison, the Woolwich Ferry carries two and a half million passengers a year, in three clapped-out ferries running not terribly often.
No, the Emirates Air Line is an unnecessary shiny thing, conjured up by a Mayor who likes building unnecessary shiny things because they make it look like he's doing something. A big red tower by the Olympic Stadium - unnecessary, shiny, ticketed. A new red bus with a rear platform - unnecessary, shiny, expensive. Barclay-blue cycle lanes across the city - unnecessary, shiny, sponsored. A floating airport in the Thames estuary - unnecessary, shiny, dead. And now a suspended advert for a foreign airline as a tourist's plaything linking nowhere useful - unnecessary, shiny, irrelevant. Of all the things £60m could have been spent on, why this?