I've also never heard of the western women converting to Islam trend, and I grew up across the street from a major mosque in a metropolitan area. Not saying it's not true, but maybe it's a UK thing? Sounds really silly, and based on little aside from the possible spin presented here, it sounds like they might be doing it as a political statement or to be rebellious rather than out of understanding, but I don't know enough to say.
However, I can say that if people ARE in fact converting to any religion for reasons aside from genuine desire to convert (or pragmatic legal necessity), I think that's a little sad.
I think that how people connect to and interpret the symbolic and unanswerable has profound effects on how you behave.
To answer the OP question, I think that people can learn from their partners, and perhaps feel that the insight their partners gain from their religion is worth converting to the same. And people adapt to each other.
Personally, I'd find it very difficult to accept a belief system much different than my own unless I saw that she was truly stronger, more graceful, more capable, more compassionate, more effective than she would be otherwise. If she led by example and turned out better for it, I'd know she had something going for her. That said, I'd be more inclined to believe that it's more HOW she behaved/worshiped/connected that would really make the difference rather than what religion it came from.