I too cringe when hearing of Wal Mart exclusives... Over the past several years, I collected the 1:18 Xtreme Detail military items made by 21st Century Toys, which were sold at Wal Mart until early 2009. If you cringe at the current level of Hasbro distribution, then trying to find 21st Century items was far worse, even during the line's heyday in the 2004-2007 timeframe. Judging from reports on the SSHQ forum, people would find new items (mostly in the midwest and upper south) and it would be often 3-4 months if at all before I found the same items in my area in central California - and I live only 150 miles from the 21st Century Toys headquarters. If the items even arrived, distribution would be sporadic. It used to drive me nuts and I let off more than my share of rants. Jesse James (another member of that forum) could probably attest the rants of myself and others who were left high and dry time and again while the same people always got the stuff.
Star Wars is a bit of a different story, however. Items usually seem to show up in my area and do so timely. I was able to get the Clone Wars Y-Wing within a week of the first sighting as well as the AT-STs and Dewbacks. The TIE Interceptors and Gunships at TRU even showed up early. There are more collectors that I have to contend with than when I collected the military items, so that makes tracking down some items a little trickier. Overall, however, I have greater confidence that I will eventually see the new items somewhere and get what I want.
That said, at least two of the Wal Marts in my area now have the AT-STs in large endcap displays with 10 or more vehicles. Dewback sets are in much smaller numbers. So far, I've only seen two Dewback sets and got one of them.