'Searches on Google and status updates on Facebook are the new mission-critical: back in the day a "mission critical" was ERP and payroll.'
This is false, although it is false in an interesting way. If I do a search on Google then I get some results: perhaps I will get the same results if I search again but perhaps not; and perhaps the results will be useful but perhaps not. Or, possibly, I'll get no results at all so I'll need to resubmit the query. It doesn't matter very much: all that actually matters is that the results are good enough to keep me using the service and that they contain sufficient advertising content that Google make money. Similar things are true for Facebook.
But if I send a bunch of money to someone from my account then it matters very much that money gets to the recipient, that either it gets to the right recipient, that it leaves my account and so on. In desperation it might be OK that none of these things happen, so I can try again. It is never OK for only some of them to happen: if my bank fails to send my rent to my landlord while taking it from my account then I will end up living in a cardboard box under a bridge.
Searches on Google are simply not mission-critical: moving money around has always been mission-critical.
The clever trick that organisations like Google and Facebook have done is to recognise that certain sorts of activity, such as search, don't actually need to work very reliably which allow for enormous scaling.