[zippy]

you, personally, may be a high margin customer, but some, and perhaps a lot, of the $5/no customers are potential liabilities due to not patching software or libraries or choosing terrible passwords for their services, databases, etc.

one decent incident can cost a multiple of a year's revenue for the account.

[jimmaswell]

is this just about cpu power from exploits?

[zippy]

no, more like someone's instance gets pwn-ed and is now part of a botnet and DO is getting calls and or isp-blocked and has to devote staff time to the incident.