Everyone has their hobbies, their interests, and their experiences. These, of course, vary... but their usually is a pattern to them.
And no, I'm not referring to the relationship to one's life story. If that's incorporated, there's always a pattern to them.
This isn't to say, mind, that the pattern is always the same... or even of the same type. Every person has their own pattern of interests.
This pattern says a lot about that person, too... but this isn't really the forum for a discussion of that.
Perhaps more importantly, there's a relationship between components of this pattern. My interest in Japanese langugage, for instance, is strongly related to my interest in Japanese culture. This, in turn, is a portion of my interest in cultural anthropology. My interest in cultural anthropology is a minor focus area within my interest in the scientific study of people. To be more specific, that particular interest extends across psychology, microsociology, and cultural anthropology. How my interests in psychopharmacology and experimental methodology tie into this should be pretty obvious.
The thing is, autistic interests tend to follow generally different patterns than neurotypical interests. The connections (and definitions!) of autistic interests tend to be different as well.
To me, there's an infinite variety in the peer-reviewed literature. By reading through it, I can learn about endless topics, find out all sorts of really neat things... it's like an infinite and ever-expanding cornucopia of knowledge about whatever obscure topic I might want to learn about. I can get lost within that for hours, days... or even weeks.
To someone else, it probably looks like I'm just reading all the time -- a "restricted" and "repetitive" interest. But... what of the main activity of many biblical scholars? What do you call it when they not only read all the time, but read the same book? Similar things can be said of most, if not all, autistic perseverations.
To put it another way, both the degree to which something is "restricted" and the degree to which it is "repetitive" are highly subjective.
Of course, this isn't to say that an unusual pattern of interests doesn't come with its fair share of disadvantages. For instance, someone who loves sports can always find someone to chat with about the latest Cubs game (or whatever). Someone who loves romance novels can usually find someone to ask if they've read any good books lately.
Now... imagine the stares I'd get if I were to just casually ask someone, "Read any good methodology papers lately?"
That is, in my opinion, the largest problem with having a "restricted and repetitive" set of interests.