in a perfect world, all the threads that make up the WOF would be at perfect right angles to the selvedge. i don't know anyone who lives in that world.
removing the selvedge has nothing to do with the grain. if the grain isn't straight, removing the edge won't straighten it out.
the direction of the grain has been processed into the fabric. whatever you do to it, it wants to default to it's original direction, like curly hair. you can wash it, iron it, whatever. but if you hang it up wet and let it dry by itself, it'll be crooked again.
i just wash it to get out the bleed (with or without retayne), machine dry, line up the selvedges without a bubble, trim the ends to match by cutting them even, iron or not, and put it away. when i go to use it, i starch the h*ll out of it to facilitate handling and go on my way. after a quilt is quilted down, everything is stabilized. if the quilt is crooked, it's not the fault of the grain.
every quilt i ever made has been able to be blocked perfectly square without worrying about grain. after all, when you make hexagons, only 2 sides are on grain. triangles? 1 side. just handle carefully and get on with it. the only time grain matters is on curves. there you want bias, NOT grain. the rest is unimportant. those directions were written before machine quilting.