I'm not really convinced of that. If your registrar folds or turns on you, it will be painful regardless of whether you also use their other services.
You're suggesting that it's somehow more likely that they will cause trouble on the registrar side of the business if you try to move away from those other services. Which may be true but should be more than compensated for by the fact that providers with a large offer of various services are also large enough not to care about you in particular.
Will OVH even notice that I stopped using 10 or 20 of their servers, have someone connect the dots, and put some sort of hold on my domain? I find it much less likely than a small (relatively to OVH) registrar operation simply folding.
What I would advocate instead is to use a really solid registrar for a high-value domain. For example, in Poland our national registry (NASK) for .pl also acts as a registrar. And while their prices are somewhat higher than the competition (~4x), it's as solid as you can get and I know people who keep their short, or otherwise cool, domains registered sometimes well in the nineties there for safety.
Using a good registrar is key but you also want to separate host from registrar because you want to keep your content.
It is a much more common case to change hosts than it is to change registrars.
But even if you lose your domain name somehow through a bad registrar your content can also hold a lot of value and though you would take a big hit by changing domain names for a lot of sites (like blogs and other content heavy types) content is key.
See the recent incident with cyanogenmod the move to .org went rather well until the .com was given back and not having a separate host can make it so you don't even need to restore from backups/setup a new environment.
> you also want to separate host from registrar because you want to keep your content.
Some diversification is, of course, a good idea. Your team chat/irc and documentation/wiki should be hosted separately, if for no other reason, then so that you have something to work with in case of an outage on your main infrastructure.
Same goes for backups. Have them somewhere else, and preferably also locally.
There are many ways to do slice it. I'm not convinced that the one outlined in the OP is really as obvious as the author implies.
You're suggesting that it's somehow more likely that they will cause trouble on the registrar side of the business if you try to move away from those other services. Which may be true but should be more than compensated for by the fact that providers with a large offer of various services are also large enough not to care about you in particular.
Will OVH even notice that I stopped using 10 or 20 of their servers, have someone connect the dots, and put some sort of hold on my domain? I find it much less likely than a small (relatively to OVH) registrar operation simply folding.
What I would advocate instead is to use a really solid registrar for a high-value domain. For example, in Poland our national registry (NASK) for .pl also acts as a registrar. And while their prices are somewhat higher than the competition (~4x), it's as solid as you can get and I know people who keep their short, or otherwise cool, domains registered sometimes well in the nineties there for safety.