why do many books on lawn care tell you to remove any leaves covering grass seed/seedlings?

The seeds don't need light to germinate, but the moment the shoots are above the surface they need as much light as possible to grow. However, if you wait till the shoots appear before raking or sweeping the leaves, you may damage the shoots, and if you remove them by hand you will probably have to tread on the delicate shoots.

Well if they are the big oak leaves those dont do good. What you really should get is some hay or thin pine needle to cover down and new grass/seed. The reason why you don't want big leaves (especially a big amount) on your lawn is that they attract pests, can cause the grass to be stunted in growth slightly and they can be a mess and harder to walk threw than a clear lawn.

Everyone I know uses straw after you rake in the new grass seed. Leaves would keep the ground wet not moist .

Straw mulch helps to protect new grass seeds by retaining moisture in the soil.

The gardening and lawn care books are telling you the right way, as you might expect if they're written by experts. Your neighbor is wrong.

To use your usual questioning technique, why would you believe her rather than them? Please explain.

Your neighbour is dead wrong. You're right - seeds need light to germinate and grow.

so many posts on the same question. leaving leaves on is good if you are growing mushrooms not lawn period.