Down Detector doesn't really detect anything other than people saying "Is [service X] down?" on Twitter, which does mean that Xbox Live appears to be permanently offline if you believe them because the typical user for Xbox Live will declare anything from tripping over their ethernet cable to a tornado levelling their house preventing a connection to mean Xbox Live is down.
It’s still useful if you remove units from the graph and treat it as a sparkline. If there are reliably ~100 Xbox Live complaints on Twitter per hour, then suddenly there are 3000, that’s an outage.
