Well that's not really true.
I worked in a shared (and dedicated) hosting company with a lot of redundancy.
Files are on netapp server (if an HDD crash, the system is just a bit slower but it's still ok and there is no data loss),
for a given plan, there is dozen or hundreds of servers (if one of them fail, the whole performance is just a bit slower, but everything is still ok),
and there is also multiple switch with multiple internet links with ospf if one of them fail.
With this kind of redudancy, there is in theory no downtime at all (just a few seconds if an internet link fail to automatically update routes), only slowdown (but when there is 500 servers for one plan for instance, when 5 of them are down, you don't notice any difference).
And i don't talk about data backup on multiple locations, with ability to recover a datacenter to another place in 24H if one of them burn (but we never had to really test this).
So, yes, you can have better uptime with shared hosting, even better than dedicated hosting.
Because when (about) everything is shared, if something crash, there is no downtime, just a bit more sharing (less performance) the time to repair.
Get [color=#CC0000]$97[/color] Off with promo code :[color=#6600CC]97USD[/color] use "moua" as referrer