Rendered images shouldn’t have to worry about that though so is it the fonts, the rendering software, or simply unavoidable in text of this size, rendered at odd angles and overlaid on different colored backgrounds?

Compared with Mapnik, I’d say Google maps look just slightly better overall but are also less consistent so can look noticeably worse when the text is at an angle.

Microsoft maps, which I don’t normally look at are an even more extreme example of this, standard horizontal text looks very nice, but it goes to pieces on winding and angled roadnames.

Osmarender has stronger text but seems to lack a mechanism for blending with backgrounds and has some extremely small text too.

So maybe no-one does it because it’s simply impossible (though my browser seems to do okay, at least with black on white text at similar sizes) or perhaps people have just become used to looking at the text as rendered by Windows and not even looked into potential improvements.