There is a difference between these words, and yes, I think it does matter.
Uninterested means that you have no interest in something; disinterested means you don't have an opinion about something. So, for example, a judge should absolutely be disinterested in the outcome of a trial (they shouldn't be prejudiced one way or another) but should absolutely not be uninterested in the trial itself.
Too often disinterested is considered to be synonymous with uninterested and is used to replace it. You might think that making this distinction is pedantic, but 'disinterested' is a useful word with a particular meaning and nothing is served by diluting it.
Words are tools, let's not blunt them.