Just like Firefox, Chrome doesn't have a smart spell checker. It uses a dictionary and it shows spelling suggestions for the words that aren't included in the dictionary. Chrome's suggestions aren't always great because they ignore the context.
Google has an excellent spell checker that's used in Google Search, but Chrome's team avoided using it because of privacy concerns. It seems that Google changed its mind and some of Chrome's spelling suggestions will be obtained from Google's "did you mean" service.
A future update will "integrate the Spelling service (a.k.a. 'Did you mean') to a context-menu of Chrome so we can see the spell-check result retrieved from the Spelling service. This change sends a JSON-RPC request to the service in the background and updates a context-menu item." Even if the suggestions can't be displayed instantly, they're a lot better than the suggestions generated by Chrome. An even better idea would be to provide an option to spell check the entire text using Google's online service.