There was a time when the 500-channel universe promised a niche for everyone, a channel to suit every taste. And for a while, that’s what we had. But lately, it seems that nearly every cable channel is sliding towards the same middlebrow pit – a show that airs on TLC could just as easily air on Discovery, Bravo, or even the once-highbrow A&E. But dumping the niche also seems to mean drawing a bigger audience, so truly distinctive channels may be a thing of the past.