I'll give this a bump to point out that I spent quite some time chatting with the Vertical people at Anime Boston some weeks back. They would like to release Leo (as well as other Tezuka works-- make sure you email them and tell them what you want, they LOVE feedback!!) but according to the reps I talked to, Tezuka Productions themselves are indeed, as cmoon speculates, quite gunshy about releasing the comics in English-- the silly/dated depictions of Africans are way more prominent in this title than in Astroboy, and the parent company wishes to avoid controversy.
Of course, the natural solution to this is simply to present the material as educational/archival-- happens all the time for all sorts of 'un-PC' older media. Vertical are confident that a Leo release would make no waves and meet with acclaim. But for the moment, Tezuka Pro are holding back on this one.
(and for the record, I asked the Vertical dudes for Wonder 3 and Ambassador Magma
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