Per your original question: You do need to have the batting and backing slightly larger for quilting. This is because the quilting process can cause some shifting and will take up a bit of the length and width of the block. After quilting you will then trim your blocks. This is why you saw them looking that way (trimmed) in the joining tutorial you saw.
If it helps, I just posted a tute on joining QAYG blocks in the Tutorials section:
http://www.quiltingboard.com/tutoria...l-t283918.html