The Real Book for vocalists comes in two versions: The Real Vocal Book for high voice or low voice. What are the actual vocal ranges appropriate for these transcriptions? The publisher’s descriptions are no help. Based on the Amazon review comments, it sounds like the high voice book may be for sopranos and the low voice for tenors, but I couldn’t find anything definitive.
I know I'm a bit late, but I find the high voice book works better for most men and the low voice book works better for most women. Yes, most vocal books are published in a high edition for sopranos/tenors and a low edition for altos/baritiones, vocal ranges for solo jazz singing tend to be different. In jazz (and many pop styles), women tend to stay in a lower range while the men sing higher in their range.
Also, the low voice real vocal books tend to have more songs in their "standard" keys (the same key they are in the non-vocal real books).