It’s common enough that I’d call it a style choice.
Garner doesn’t mention the topic, which is surprising.
MWDEU calls it “the chief variation” regarding apostrophe use, and says “some writers” do it.
The Cambridge Guide to English Usage gives the most explication of the issue. It outlines four different practices:
1) Literary, classical, and religious names get the apostrophe only, all others apostrophe s (e.g., Keats’ and Jones’s)
2) As above, except only names of more than one syllable get the apostrophe s (e.g., Menzies’s, Keats’s, and Jesus’)
3) Any name ending in a “long ‘eez’ sound” uses an apostrophe only (e.g., Jones’s and Xerxes’)
4) Any name whose possessive is pronounced with the same number of syllables as the plain form takes only the apostrophe (the guide points out that this one is the most problematic, as pronunciation varies)
Pullum and Huddleston are most on point. They say, “there is a good deal of variation here and it is not possible to give hard and fast rules. The bare genitive [i.e., apostrophe only] is most widely used with classical, religious, and literary names [...]. Elsewhere it is normally restricted to names pronounced with a voiced /z/ rather than voiceless /s/ [...]. Examples like Ross’ are sometimes attested but they are of questionable acceptability; Ross’s is the normal form, and in speech the /iz/ is required.” Simply substitute Daniels for Ross in their example.
Editing Canadian English says, “there is little agreement in the treatment of the possessive of proper nouns ending in a sounded s or z.” [This book also notes that many corporate names in Canada omit the apostrophe where their name would traditionally have it in order to comply with Quebec’s language laws, which forbid the apostrophe in such cases. That of course isn’t relevant to the topic at hand, but it’s very Canadian.]
It violates MLA style.
It violates Chicago style.
It violates Oxford style.
It violates Australian government style.
In summary, there doesn’t appear to be any regional variation in the practice. It’s muddled everywhere that English is written. The only consistency seems to be found among professional publishing houses, who would require Daniels’s Butler. But movie studios aren’t obliged to follow the follow the style manuals of publishers.
In the case of movie titles, I would suspect that the graphic artists designing the posters and ads have more influence on the subject than the copy editors. The choice will be to go with whatever looks cleanest and best, rather than traditional editorial rules or how the words are pronounced.