You'd expect them to be monitoring more than just the HTTP response codes from user requests for precisely this reason.
If the first they hear of an outage is when user requests start to fail, then that's a failure in their monitoring as well.
But effective monitoring is harder than people assume.
> But effective monitoring is harder than people assume.
Who says public status page equals internal monitoring.
They likely know faster than you. Whether they post it publicly is a different issue (hint: SLA penalties, news impacting stock etc)
> If the first they hear of an outage is when user requests start to fail, then that's a failure in their monitoring as well.
Isn't that what monitoring actually is? The issue seems to be in their testing, not monitoring.