Similar sounding bands.

Any genre can sound "all the same" to a listener not into that genre, including Bluegrass. It takes some listening experience to develop the discernment necessary to discriminate between the practitioners of some music. If one doesn't like a particular genre, he or she won't invest the time necessary to do so. LOTS of people don't like Bluegrass, or even Country.

I like all styles including country. I also realize the skill you need to have to perform bluegrass! I can spend a time to listen to one or couple of bluegrass songs and tunes and even enjoy that, but after being at bluegrass festival, I realized all songs and bands sound same and bass can be done via computer for all bluegrass songs. Same notes, same rhythm, same harmonies, same instruments and very very often SAME WORDS too. It doesn't need to be into or not into it just same all over.  

Susan Tedeschi and Bonnie Raitt have similar sounding vocals and vocal styles, IMO.

Parquet Courts (Quarts) and Velvet Underground

Well then czarivey, you should know that The Del McCoury Band sounds quite unlike The Steeldrivers, that The Delmore Brothers sounded nothing like The Dillards, that Ricky Skaggs sounds very different Tony Rice, that Alison Krauss sounds little like Rhonda Vincent, that no one sounds like Iris Dement or Dolly Parton (she's been doing Bluegrass for about fifteen years now, as apposed to her Country-Pop schlock), and etc. I would say that any two white "Blues-Rockers" sound more alike than any of my Bluegrass examples. There are many, many more of such I could (and will, upon request ;-) cite.