A friend asked recently about whether it would be a good idea to move their company domain to the same discount hosting they use for their personal website. My reply was that it was fine to move the hosting of the website but that it was a bad idea to move the domain registration to the same place that hosted the site.
"Can we leave the domain registration at the registrar and still move the hosting? And why is it bad to move the domain registration to the hosting company?" was the response.
The bottom line is you should never, ever, absolutely never, have your domain hosted with the same company that is the registrar for your domain. If you have this today go change it now and then come back to read why you got lucky.
Two centuries ago when the revolutionaries were making themselves into founding fathers of the United States they had the concept that one should keep power and responsibility divided amongst different branches of government. This serves several purposes including making sure that one bad apple doesn't ruin the batch. Even a collection of bad apples need to get the consent of plenty of other actors before they can ruin the batch.