Does brining a chicken/turkey before roasting really make a difference?
Assuming you don't normally buy pre-brined / injected birds, you should notice a difference... As roux notes, it should be noticeably moist and tender, especially the white meat.
A couple of things to try:

Increase the time in the brine. 10 hours is plenty for breasts or quarters, but a whole chicken may take longer. A whole turkey will definitely take longer!
Check your salt. A cup of small-crystal table salt per gallon of water should be fine, but if you're using flakes (kosher and some sea salt), you may be producing too weak a brine! If in doubt, weight it out.

See also: What are the basics and options of brining meat, for example chicken?