By the way, Germans had a slightly different definition of who was a "Jew" in each occupied country.
In Poland Germans applied a distinction for "Jews" and "Jewish cross-breeds" (in Germany they had "full Jews", "1/2 Jews" and "1/4 Jews").
According to the ordinance issued by Hans Frank on 24.07.1940, a "Jew" in Poland was the one whose either three grandparents were "in racial terms" (in practice it meant grandparents whose ancestors adhered to Judaism, unless a person had a "typically Jewish" look) of "purely Jewish" extraction / descent, or whose two grandparents belonged to a Jewish religious community. While a person whose one or two grandparents was / were of "Jewish descent", was according to German definition a "Jewish cross-breed". Also companies were recognized as "Jewish" if at least one or more of their owners was / were Jewish.
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Let's also quote data from Polish 1931 census on mother tongue / ethnicity among Jews in Poland (all numbers in thousands):
1) Adherents of Judaism (also called Israelites or adherents of "Mosaic confession"):
Total - 3113.9, of whom (mother tongue / ethnicity):
Polish - 371.9
German - 6.8
Ukrainian - 0.2
Ruthenian - 0.3
Belarusian - 0.2
Russian - 0.4
Jewish* or Hebrew - 2731.4
Other or not given - 2.7
*Can be also translated as Yiddish.
2) Speakers of Jewish or Hebrew mother tongues who were not adherents of Judaism:
Total - 1.2
Grand Total in these groups: 3115.1
As you can see Polish Jews were very religious, compared to those in other European countries.
Apart from high levels of religiosity, Polish Jews also preserved a high level of linguistic distinctness. For example vast majority of Jews in France (who were less numerous than Jews in Warsaw alone) spoke French as first language and dressed like their French neighbours (as most of French "Jews" were not religious, let alone religiously Orthodox). That wasn't the case in Poland. Majority of Polish Jews were Orthdox Jews, dressing in traditional Jewish clothes. Most of them were bilingual and could speak Polish, but not as their first language (mother tongue) and thus with heavy Jewish accent, often also not fluently enough. As of 1931 only 12% of Polish Jews spoke Polish as their mother tongue, primary language. That proportion perhaps increased** to 15% by 1939 (my guess).
My guess is also that majority of Holocaust survivors in Poland were people from among those 15% of best-assimilated, Polonized Jews. Not only because attitudes of Christians towards such Polonized Jews were different (much warmer, since there was no sense of "alienness" typical in relations with very religious and very traditional Jews), but also because their skills - perfect knowledge of Polish, indistinctive dress, different environments in which they lived (usually in Christian or mixed neighbourhoods), etc. - were making their chances to survive much bigger than those of Orthodox Yiddish-speaking Jews.
**Since 1918 Jews in reborn Poland were gradually assimilating into that nation. There were Jewish circles who favoured assimilation and full integration with Christian Poles, but there were also traditional circles who opposed any integration and considered intermarriages with "goys" sins.
