I think that the argument is that since the data center is "reliable enough", you don't feel the need to adequately test your failover option/procedures. If you knew that your data center would go down more frequently, you would better test your failover.
The question then becomes, when is it economically more viable to use multiple low(er) availability data centers as opposed to one hyper available one? (And since you should be designing for data center failover anyway, that is a fixed cost).
The question then becomes, when is it economically more viable to use multiple low(er) availability data centers as opposed to one hyper available one? (And since you should be designing for data center failover anyway, that is a fixed cost).