Yea sorry if I came across rude, didn't mean to attack you or heroku, just wanted to set the figures straight.
With regard to heroku you have a point about the "not needing a sysadmin" part. That, however, only works for a fairly short period during the lifecycle of a business; heroku is ideal for bootstrapping.
Once your site grows to the scale that mark is seeing (if that persists, which I doubt) then the heroku value proposition rapidly shrinks.
At that point you start to need more customization than heroku can provide [for a reasonable price] and you also need at least one person with systems knowledge in your company to prevent expensive mistakes in the software architecture.
Gladly that person will then more or less pay for itself, simply by moving the app to a cheaper hosting platform.