Earlier quoted context omitted.
HDTV indicates source, not release quality. It's the same with bluray. The naming standards (and everything else for that matter) are highly regulated which is an impressive example of order by consensus since no one can give out orders. RARs are an artefact of FTP transfers during which files would get corrupted, and not-so-fast connections of the past which made re-downloading the whole release somewhat inconvenien…
I thought that rar was used so that the capper could split the archive across multiple files and begin uploading the content before the show was over.
There used to be a group named NOsegmenT who were staunchly opposed to the practice and included a little diatribe against it in all of their NFOs.
Also bear in mind that some groups have (in the past, at least) had pre-air sources. LOL/DIMENSION, one of the most well-known TV groups, were called out on the practice of obtaining shows from a pre-air source then manually adding television station graphics a couple of years ago. They would "pre" their releases almost instantaneously after they finished airing.