Granny writes:
In the US, about 40% believe evolution to be true, yet only about 4% are non-religious.
About 15% are non-religious, Granny. Your link actually agrees with that, and it fits what I've found over the last few years. The non-religious are by far the fastest growing sector. About two thirds of them are non-theists, and the other third vague deist/theist types (probably where the Percys of this world fit in). That's why the often quoted statistic that 90% of Americans believe in God is also correct.
An easy to remember approximation is:
75% Christian, 10% other religions, 5% deist, and 10% non-theist, with the last two making up those who will tick the "no religion" box on questionnaires.
Note the interesting stats for Judaism in your wiki link. Jews have the highest education levels, and the religion's being decimated. About 20% are non-religious, and 25% have left for other religions (hardly surprising, as about 50% are marrying non-Jews).
You're right, of course, in saying that there are more theistic evolutionists than non-theistic evolutionists. Actual self described atheist evolutionists may be only 5% of the population, making the creationist view that evolution = atheism look ridiculous (like all their other claims, when you think about it
).