An hours outage can happen to any system.
But what if it were 24 hours?
Or what if the supplier went terminally (oops!) bankrupt over night?
The only secure way to handle data required by lots of people, widely distributed, is to have a "core" database, from which each person downloads what they need for the day, and downloads further updates as and when necessary, and transmits their own updated data to the centre as opportunity presents.
Nobody seems to wonder what happens if your sales force need to go where there is no mobile net access.
I always carry my own essential data - my Psion 3a is in my pocket.