These are all great questions.
Tim, while not working for Moodle HQ has answered them very well - Thanks Tim!
The goal of MoodleCloud is to help as many users as possible get started with a Moodle site. It's a service that allows anyone to experience Moodle within minutes and helps users build a Moodle site to a certain level (500 users and 1Gb of file storage).
As we offer limited support, we feel once you get to that level, you are ready for that next step and Moodle Partners can offer a more tailored solution and provide the necessary support and assistance for hosting a large site.
As Tim mentions, the flexibility of Moodle means you can shape the solution that's right for you and choosing an appropriate hosting option is part of this. So it's likely that Moodle hosting will continue to will come in many shapes and sizes from many providers.