AFAIK, it is possibel to disable phpinfo() since my ISP have done the same thing however I get a different error text back (it's more stylised telling me about security implications).
I have also seen some settings in my php.ini script which limit information displayed by a phpinfo() dump, so it sounds like a reasonable assumption.
The reason would undoubtedly be for security to stop someone getting lots of information about there server in one dump on a webpage 🙂