How do you figure? 99.99% of the time our clients expect us to be up, we're up. We're not the electric company; if we're up the right 166 hours in a week our customers aren't impacted.
If you turn your monitor off at night, does it suddenly have 70% availability/reliability?
99.99% availability is almost always predicated on 24/7 uptime numbers, not 24/6 plus an extra 22 hours.
If you say to someone "We have four nines of uptime", and they ask how you apply kernel patches, and you say "oh we just do it during our 1% of downtime", they'll boggle at you, and for good reason.
If you turn your monitor off at night, does it suddenly have 70% availability/reliability?