I suspect that the documentation has not been amended for ten years or more! It probably goes back to the early days of open data when there was a real debate about how useful it was for an organisation to know its customer base. For example, if someone asked me for a statistic, my first question was what are you trying to shed light upon, because often there was a better approach, the statistic wasn’t capable of answering the question or (remember some queries originated with ministers) it was the wrong question! That opportunity goes if the dataset is downloaded without interaction or registration. It quickly became clear that those disadvantages were outweighed by the advantages of “letting a thousand flowers bloom” in terms of reuse. (There are some stories that could be told about those early days…). There is some contact with users through fora such as this but no doubt there are other unknown users out there.
I can see no reason at all why any static dataset should require registration. The sort of stuff people do with the dynamic datasets such as Countdown is another matter as it has resource implications.
The xml files in this particular zip file are, I believe, to be updated to use a new version of TransXChange at some point. If this is going to affect the format or content of the files, It would be good to have confirmation that users will be able to see a test example in advance.