Nice project, fun write-up!
But I have to admit, I don't see such huge differences in the rendering.
Two readers ignore your choice of font; that might be because of your spelling of "sansserif", which I have only seen spelled with a hyphen in stylesheets so far.
FB Reader ignores your hr-break, but last time I checked (it has been a while, admittedly) FB Reader ignored nearly all formatting anyway.
It's a weird choice, by the way, to define font-size in pt. Try em and perhaps you will get a more consistent look.
And if you ever publish an e-book: Please please please don't define text-align at the paragraph level; that makes it impossible to override without changing the stylesheet, and people with taste (
) can't be expected to read a longer prose text left-aligned
EDIT: Oh, and best wishes to your uncle.