Some experiments, all under hu: in Wikipedia. A possible conclusion is that some API limit is broken at pages with long history while for short histories the results are identical.

site = pywikibot.getSite()
page = pywikibot.Page(site, what)
print len(page.getVersionHistory(getAll=True, reverseOrder=True))
print len(page.fullVersionHistory(getAll=True, reverseOrder=True))

what = u'Földvár (építmény)'
68
68

what = u'Triatlon'
127
127

what = u'Magyarország' (This is the "Hungary" article in huwiki with many edits.)
3510
812

what = u'User:BinBot/try' (This is not big but has several edits. In this case getVersionHistory() also takes some minutes!)
53833
2902

what = u'Wikipédia:Kocsmafal (egyéb)' (This is the main village pump of huwiki, several times edited a day.)
48155
156

In the last two cases getVersionHistory()was very slow and fullVersionHistory fast but erroneous.

what = u'en:Triathlon'
2039
893

what = u'de:Szeged'
528
528

what = u'de:Berlin'
7041
912