They don't happen very often, although I had one just the other evening. It's procedure, you really don't tend to get crews making up their own SOP's such as that. Generally, you will find it happens whenever there is an auto land and I believe this is a CAA requirement here in the UK rather than something that is stipulated by individual carriers, though I may be wrong.
As for taxiing in, i'm not sure why that is procedure but it might well be something simple like keeping passengers strapped in rather than fumbling for electronic devices.
If posed correctly, I'm sure the crew would have been more than happy to answer any questions you may have.