You can never get over 99% is technically impossible
It is easy to have over 99% uptime, and all hosting SHOULD provide greater then 99% uptime.
99% equates to 14 minutes and 24 seconds of downtime every day or 7 hours 18 minutes and 17.5 seconds of downtime every month! That is terrible!!!
99.99% equates to 8 seconds a day, or 4 minutes 23 seconds per month. This accounts for the need to occasionally restart a server or replace hardware.
I will argue that guaranteeing 100% is not possible, as servers do occasionally need to be restarted and hardware does occasionally fail. However quality providers should be able to provide 100% network uptime.
Now a days is easy to have backup servers, you just need a fast dns and a fail over, you can reduce downtime to under 10 mins if anything happens.
Keep in mind, not all DNS servers honor the TTL that you set. Therefore you have have a TTL of 10 minutes, but some ISP may still send users to the old IP for hours after.
If you need high availability and failover, your better off with your own load balanced cluster with heartbeat monitoring. This configuration, on a collapsible core network will give you as close to 100% uptime as possible.