From my research the ridiculous ratios like 1:800 are bunk due to a few factors:
1. I found that ratio was often a pure help desk count (1 help desk to 800 employees) and left out higher skilled staff driving business forward or maintaining systems (Admins, manager, etc weren't part of this number)
2. People mistakenly consider employee count vs. user count. I worked at a company with 2 IT staff to 600 employees. Sounded impressive except there was only about 40 computer users there.
3. Larger orgs often have their software/servers managed by corp somewhere else. That 2:600 org? They didn't manage ERP, CRM, or even the network firewall. That was all corporate. They basically fixed computers, managed user accounts, and ran some SQL reports for Marketing.
4. Services offered is a huge factor people ignore. A company with 200 people running Microsoft Office could be pretty easy for one or two people. A company with 50 people running CRM, ERP, controlled environment monitoring, reporting, custom apps, QMS, phone system, e-commerce, website, and integration between them all? I've seen 4+ IT staff at those places.