It is indexed by Bing... and a minor change to the query will definitely result in WW as #1.
Yes, I noticed it in Bing this morning, with the three-word search as #2. Adding the zip (as in the original search) puts WebmasterWorld at #1. Note that this thread doesn't come anywhere near ranking for [sunday hours] by itself.
Some thoughts about how Google and Bing are treating this query (and forgive the length in advance), trying to oversimplify a complicated subject...
If in a query I misspell a word in a way where the entered word is nonsense and the correct version is predominant, both Google and Bing automatically display the corrected version and ask if I really do want what I originally typed.
On queries where there simply aren't very many good results, Google will look for alternatives. If appropriate alternative results exist, I'm seeing that Google will modify my query sooner than Bing will. Even when the problem is not spelling, Google will often reach for another word with a similar spelling when it can find one within the context of the query. Going further, Google will sometimes rewrite my query to include a synonym... or sometimes even include a result that contains an antonym of my original terms... if the context is right and there's no better match.
In this search (for which there's really no satisfactory result), we're dealing with several pecking orders, one of which is vocabulary matching... another of which is context... and another of which is branding, which Google reduces to "trust, reputation, authority, and PageRank", along with social buzz signals. Google, I'm thinking, for this query felt that vocabulary matching, which here includes the zipcode, didn't produce a useful result, for reasons martinibuster has pretty well described. "Sunday hours" by itself is so incredibly general a search that the engines have got nowhere to go except for the most statistically likely companies, big brands which are what both Bing and Google suggest for 'Sunday hours' related searches.
Again, the only exact match on the web for the query as a whole is on this thread... so Google must make a choice among iffy signals to deliver results most likely to satisfy the largest number of users. I'm positing that Google added some brands into the serps that are contextually associated to the zipcode and with the term "dermatology" part of the query. These are associated statistically via phrase-based indexing, and also via links from directory pages which come close to the vocabulary of the query.
With regard to the context, my guess is that contextual matching in general on Google is currently set on the high side, and Google will often go too far afield in its suggestions, particularly on longtail queries. I'm thinking that this may be a purposeful choice, as a way of speeding machine learning along... at least I hope that's where it's going. ;)
I'm also thinking that the best indications of what Google's AI has "learned" so far are indicated by Google's autocomplete suggestions, and that one of the suggestions Google does make...
dermatologist open on sunday jupiter fl
...is closer to the question that brinked said he wanted to ask...
I was looking for a dermatologist that was open on sundays
...than what he entered into the search box...
33458 dermatologist sunday hours