The main idea behind polaroid sunglasses is that reflexion from water, snow and other glary reflectors is mainly polarized in one direction. To understand this, witness the behaviour foretold by the Fresnel Equations (the graph below taken from the Wikipedia "Fresnel Equations" page):
so that you can see for a wide range of scattering angles from these surfaces, the reflected light reaching your eyes is mainly in the $s$-polarized direction (electric field vector orthogonal ("senkrecht" in German) with the plane of polarization), so if you quell this polarization, you get rid of most of the glare from these surfaces.
Why are your lenses twenty degrees off in their polarization axes? I'd say that this is a simple question of production economics. The power through a polaroid varies like $(\sin \theta)^2$, where $\theta$ is the angle between the actual polarizing axes and their ideal directions for quelling a given linear polarization. This functional dependence is very flat for a wide angle range around the null, so, if there is a twenty degree error, the attenuation ratio is still 0.1. So a polarizer that is twenty degrees off is still almost as good as an ideally aligned one for the lower-the-glare-in-human-sight application. Therefore, a manufacturer simply will not go to the extra cost of the quality control needed to align the polarisers more accurately: it really wouldn't make the product any better for the application at hand.