That is the marketing statement, yes. But the technical implementation is somewhat more complex and possible to bypass than your boilerplate comment suggests.
The technical implementation is called the sandbox, and it's a fundamental part of iOS security. Yes, it is possible to bypass the sandbox, but it would involve exploiting security vulnerabilities on the user's device, which Apple offers up to a $25k bounty for. You generally have bigger problems if something escapes the sandbox on your device, though :)