That’s what I surmise from a list of iPhone OS 3.2 SDK features listed over at Engadget.
Included dictionaries: Apple Dictionary, New Oxford American Dictionary, Oxford American Writer’s Thesaurus, Shogakukan Daijisen, Shogakukan Progressive English-Japanese Japanese-English Dictionary, and Shogakukan Ruigo Reikai Jiten (may also be used for a Dictionary app perhaps?)
I understand the need for a dictionary for Pages. That’s necessary for spellcheck.
But with a dictionary baked in the OS anyway, adding dictionary word lookup to iBooks wouldn’t be a difficult thing.
Models of the Sony Reader with dictionary word lookup use New Oxford American Dictionary and Oxford Dictionary of English.
The Kindle uses The New Oxford American Dictionary.
The Barnes & Noble Nook uses Merriam-Webster’s Collegiate Dictionary.
Also important:
Much richer text API including low-level access to font data and highlevel support for drawing formatted text
I don’t know if that will help eCrap ePub any. I suspect it’s more for a future use.
The eBook Test 
Unless they have changed it in a recent update, BN Nook does not use MW Collegiate Dictionary. It uses a Pocket Version. Which means practically any word I have wanted or needed to look up is not available in the dictionary.
I took the Nook dictionary info directly from B&N’s own site.
You’re right to point out the API support for font and drawing formatted text in the Engadget article. That is indeed important.
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