That's not exactly the same as buying something with Bitcoin. XAPO is basically like exchanging Bitcoin for fiat and paying with fiat. There are some airlines literally accepting Bitcoin though. Hopefully others will follow suit in the near future.
I think we need to accept that currently the world revolves around fiat..there is no escaping that fact..99.9% of commercial transaction in bitcoin get converted to fiat eventually. whether it be remittance, purchasing goods ,paying bills, speculation or buying airline tickets.
Many are hoping for the day when bitcoin received for payment will be held just like any other form of currency eg dollars received for payment in Japan held in a dollar account for the long/medium term.
In order to get to that point being able to pay with bitcoin whether directly to an airline or merchant who then converts to fiat or using a Xapo type card which converts at time of purchase is part of the journey ( and is really the same process but in a different order and timing of conversion) until it achieves its status as a currency to be held on to.
The advantage of using Xapo instead of dollars or dollar denominated cards is a) it can be competitive or even cheaper to use if purchasing outside a dollar denominated country b) you are still holding on to bitcoins in your "account" and will reap any reward from increase in fiat value of the bitcoin. Conversely you are exposed to adverse moves in the fiat price so this is for bitcoin bullls not bears.c) you are actively promoting bitcoin in order to eventually get to the stage where more merchants accept bitcoin directly and do not convert to fiat and hold those bitcoins as they would any other foreign currency of strength.. eg in Argentina dollars will not be converted to local currency with a 40% inflation rate but kept in dollars or dollar accounts. the big advantage for bitcoin in this case is that if currency controls are introduced where you cant move dollars out unless you smuggle them bitcooin can circumvent that problem with ease.