Many apologies for the delay in responding Richard,
In a nutshell, yes all the services feed off of the same database although it can take some time (on occasions) for all output mediums to update with new / fresh data.
Also, the newer API is cloud based, whilst the legacy ones are not.
The main advantage of the API is that its a recent product using a platfom we are standardising on and one that will continue to be updated with new features, and of course is completely free of charge.
The XML gateway, being a legacy service, will be closed in due course but there is no timescale for this yet - at this time, it has a more comprehensive name checker facility than the API does.
I hope this clarifies.