I think GP's point is that you should assume the 0.{however many 0s}1% it's down is going to be a bad time for you, and then ask yourself how long you want to wait to be back up.
A long down time might be worse for you than a shorter down time more frequently.
If this service is up for five years, then it can go down for 15ms and still claim all ten over that period. Which is almost nothing still, but if you needed ten to begin with then maybe it's quite a lot for you.
All I'm saying is - and I think this is what the commenter originally twice above me meant - is that the rate doesn't give you all the information, you at least need a period as well.
A long down time might be worse for you than a shorter down time more frequently.