BBC2 and Channel 4 used to specialise in showing great B&W and Continental films. Now, it's all about sex, beautiful young people and bizarre documentaries.
For several decades now C4 have been showing the same 2 or 3 dozen B&W films.
ITV hardly show any films now and BBC1 only show a few more. I remember the days when the Beeb used to show a couple of films a day.
Actually there's some debate as to why Hitchcock filmed in black and white. Some reading I've done on the film suggests it was because he didn't think he'd get it past the censors to show the blood in colour; others suggest that Hitch made it on the cheap with his crew from the TV series he was also making at the time (Alfred Hitchcock Presents...).
Whichever the reason, its still one of the best horror films ever made, if not one of the best films of all time regardless of genre.