Fluency is a proxy for reading comprehension, and a surprisingly good one, considering that they are not really the same skill, but still only a proxy. What it actually measures is decoding fluency. Where decoding skills pretty much level off late in middle school, an 8th grade level wpm just says she's achieved mastery in decoding. (This assumes she was reading 8th grade difficulty level text, BTW.) There are much better standardized measures of reading comprehension, if one wants to put the time and expense into it (the TORC-4 comes to mind), though none as efficient for school/class-wide screening as a one-minute reading fluency probe.

...pronounced like the long vowel and first letter of the alphabet...