There are dozens of reasons a child can be slow to learn how to read. They could have not have access to education. They could has poor eye sight. They could be malnourished. They could have difficulties learning in general. Dyslexia means "Slow to learn how to read, despite no obvious influencing factors." It's a bit of a catch-all. There might be treatments for dyslexic children that also help other children learn how to read, but it's likely that non-dyslexic children will need treatments that will not apply to dyslexic children.
Dyslexia has more than 3 million cases in the US every year. It's common. When given the right treatments their quality of life can be improved greatly. I do not want to remove the classification of dyslexic, because it might jeopardize the way those children receive treatment.
EDIT: "Dyslexia has more than 3 million cases in the US every year." You can see the dyslexia in my writing style right there....