Is 'useable' preferred in certain regions, or just an alternate spelling of 'usable'?

I rarely use spell checkers, but today when I did use one, it suggested changing the word 'useable' to 'usable' (i.e. to drop the first 'e'). This seemed immediately intuitive and I thought I'd just made a typo, but at second glance I wasn't so sure.

I haven't been able to find anything definite, even after searching this site, which surprised me a little. I've searched dictionaries and most seem to have "useable" as an alternate spelling of "usable" or simply link to it. But since my first instinct was to write "useable", I'm wondering whether "useable" is perhaps preferred in British/Australian/NZ English while "usable" is more American. This site seems to suggest the latter, but claims that both are used in British/Australian/NZ spelling. Or is "useable" perhaps simply a more archaic form that is less popular nowadays?

Could anyone shed some light on this?

When you switch to the World English version of Oxford Dictionaries Online, their definition of usable has this little "spelling help:"

Usable can also be spelled useable, with an e in the middle: both are correct.

The US version simply lists useable as an acceptable variant of usable, and omits the side note.

Etymonline shows usable as being derived from the Old French usable. It further notes that the word was "not common before c.1840," so it would seem that useable is not an "archaic form" that fell into disfavor.

I would guess that useable came to be an acceptable variant because of standard usage. I would note, however, that some dictionaries do not list useable at all.

Another answer has already mentioned how usable and useable are treated in different dictionaries; in this answer I say nothing of that, and only address relative frequency of use. Ngrams for usable,useable in both the American English corpus and in the British English corpus show that since the late 1800's usable has seen frequency of use 8 to 10 times higher than that of useable. (Earlier usage ratios are undependable because of the small number of instances, and because many or most of ngram's early instances for usable are bogus, caused by mishyphenation of words like excusable and confusable.) That is, current usage in both American English and British English strongly favors usable over useable. Of course the case may differ in Australia or New Zealand.

The onlinegrammar.com.au source mentioned in question offers usable vs. useable as a specific example of suffix -able vs. suffix -eable, saying "Both are used in Australian, New Zealand and British English. American English uses -able." That observation may remain true even if the site has picked a bad example in usable vs. useable.