It makes it impossible to track issues when you cannot see what servers are online or offline and what's going on.
I'd recommend to forbid using nginx for load balancing at your companies, only use HaProxy.
I feel they chose rather well with status pages–it's a feature that's useful, yet leaving it out doesn't cripple the OSS version in most use cases.
I don't think you realize how important are status pages. That's like the single most important feature in a load balancer, after the load balancing itself.
You cannot perform any troubleshooting without it. You cannot see servers which are online or offline. You can't see what or how many users are online and where. You can't have statistics, bandwidth, connections, health checks... nginx is a black box.
Paying for nginx is a short term solution that causes more troubles. Next you have to count licenses and distribute license keys and use the paid installer from a special source. The long term solution is to ban nginx and use HaProxy instead, same stuff without paywalled features.
If I want to put money on something, it's going to F5 or NetScaler, or ELB, or Google load balancers, or Akamai, or Cloudflare. Not nginx.
But if load balancing is your killer feature, maybe it is the wrong choice.
It's less critical for a web server doing only one thing (a static folder or a single app). However, you still can't get metrics like time to load a page, connections per second, cache hits, error rates, etc... because nginx doesn't expose its metrics (for use by graphite/statsd and equivalent). Metrics are a paid feature, $1900 per server :D
Or look in the logs. Or have your monitoring system tell you what is down, the moment it goes down?
It's a good feature, it's not an absolutely critical stop the world women and children first feature.
By the way, nginx doesn't format logs properly. You think that a HTTP status code is a number? Nginx will give you "-" or "503,503" as well. Not sure if the paid edition have correctly formatted log.
Your monitoring system can't integrate with nginx. nginx doesn't expose its metrics as I just said in the last message. You need to pay nginx plus.
A poor man's solution could be a bash while loop with wget and sleep, hitting the actual servers or just the nginx frontend. A better solution would be any one of the hundreds of monitoring systems you can pick from that do exactly that, and integrate with nginx.
And yes, those are valid values for status codes. A tad surprising at first perhaps.
Nginx exposes logs. Your monitoring system can handle those logs. A simple tail and a grep for 'Upstream server failed' in the error log would be fine. Better than manually opening some custom gui that offers the same info, just in a worse format you can't work with.
It's considered a black box because it's a black box. A hobbyist would learn to use the status page from time to time, if there was a status page. Instead, he's learning that software are black boxes and won't look for status page in his next endeavour.