Yes, it's clear that Rails blazed the path for Merb. At the same time, the Rails people really shouldn't be surprised (or feel badly) that their "opinionated software" has created a market for flexible, agnostic software.

Both projects are great, and will probably appeal to different sets of developers. In a lot of ways I think of it like the dynamic between Python and Ruby. Both are excellent languages with very similar capabilities, yet they appeal to different developers. It's like there's an element of personality in there, and there's nothing wrong with that.