As the title is written ("Why is HD locals so important?") (and ignoring the Rules for proper capitalization of Titles), if Van had said, "Why is HD Locals so important?", then the collective noun would have been understood as "HD Locals", whereas the lowercase "locals" implies the channels as individual channels and deserving of the verb "are". Really, though, it could go either way.
I know, let's have Van post this verbatim over at AVS and see what the Forum Mods have to say...